I need to help my s/o write a business grant (it may also involve helping inner city youth through the business.) I have no idea how to write one or where to begin. Where do I find legitimate instructions on grant writing and how do I find out what kind of grants are available? Any help would be enormously appreciated. 
The Sacred Chao
This is not the easiest thing to answer. First and foremost many grantors only give at certain times, and to stricly non-profit organizations. Meaning the company would have to hold a verified 501 C-3 tax status to accept monies as a charity. Without that, it is very difficult to get a grant.
As for your SO. I would look into the city you live in, neighborhood relief funds, or gov’t monies allocated to the city or town, and see if they have established grants you can apply for. Most major cities and towns do, and they tend to be a little more lenient on the tax bracket facet.
As for the actual writing of a grant…if you have never written one it is very difficult to really spell it out…Essentially, most grants have a set of written guidlines and they must be followed to the ‘t’ . No spelling or grammar issues what so ever, and make sure the narrative explains very succinctly why the organization should give You the funds…and not the program down the street doing the same things as you…
We are writing a science grant right now (due date is October 1st). It is an NIH R01 grant application. For these, there is a template at the NIH and as Phlosphr says, it is followed to the letter. The hardest thing is cutting it down and getting it to the proper word and page count.
I would stress that you find other successful (and if possible unsuccessful) grant applications similar to the one you want to submit. Reading a bunch of grants is really the best way to prepare for writing one.
Solid advice.
I’d add to it the idea to put yourself in the place of the reviewer. Write the grant, not to say how wonderful the program is on a wide number of fronts, but to say, “This program will fulfill the objective you have in giving out the money by doing X, Y, and Z that are called for in your goals statement.” And spell out how each element of the program will effectuate the grantor’s goals in giving grants.
The first thing you need to do is find a grant. Don’t write one before you do so - as others have mentioned, nearly every foundation out there wanting to give out money has a very specific set of guidelines and forms you need to comply with. It’s easier to write the application with that in mind than trying to smash a pre-written round application into a square set of rules (if you get my meaning).
Call your local community foundation to get information on what organizations have available grants, and then write to those organizations requesting their grant information/requirements.
There are also reference books in libraries that list the larger, established grants. Most such books index the grants in multiple ways, including subject area of the grant. It’s not a bad place to start. Internet searches can pull up some grants as well.
I am not sure if it will be easy to obtain the two elements of your grant - business funding and supporting inner city young people - through one grant source. Typically the latter cause would attract charitable, trust or government funding, and many trusts, foundations and the like will not give to businesses. If you are sure that you will want the two components, you may want to break the programme down into two discreet projects, and find a community or voluntary sector organisation to work with you as a partner on the work with young people (enabling them to bid for trust or foundation funds).
Chris Carnie’s book “Find the Funds” sets out straightforward guidelines on how to set out exactly what you want to do and then find a suitable funding source. Although targeted at charity fundraisers, it has some basic principles that will help with business grants too. What’s been said in this thread already is sound advice, and will be helped by you making a clear and compelling case for what you want to do in your application. The key question is what are you trying to achieve through the funding, and what difference will it make to the beneficiaries, whether inner city young people or the busines. Many funders offer a great deal of help and support for potential applicants, and searching out this information will avoid wasting your and their time with unsuitable or inappropriate applications. If you target your application appropriately, the chances of success will be much greater. In the UK, I know that applications made to trusts have a success rate (not always for the full amount requested) of around 60%, and the chances are much better with trusts that offer some form of pre-application advice/expressions of interest, prior to applications being made.
I am not sure where you are based, but in the UK, I would suggest using the major directories including the Directory of Grant Making Trusts and Corporate Giving. As stated earlier here, most directories of this nature enable you to search by location or by topic (and often both) which should give you a shortlist of potential sources. Larger libraries will usually have these directories, or you can use a wide range of web resources to identify funders for your shortlist. Business Link would be my starting point for finding small grants for the corporate part of your funding. If you are based in the US, try a search for fundraising support or philanthropy; there is a national body which supports fundraisers, of which I can’t remember the name (Institute of Philanthropy?), but it’s linked to the World Fundraising Council. Your government departments with responsibility for supporting business development or the community and voluntary sector should also have information on their websites to help point you to potential grants.
Once you have found some prospective funders, there will normally be help or support available to you from that funder through telephone helplines, web guidance or a phone number to call for guidance on whether what you want to do meets their criteria for funding.
Finally, my experience of fundraising (both as a grantmaker, and working for a charity that supports fundraising best practice) has been that it is easier to find funding for a great idea, than for an opportunistic idea that emerges in response to the terms and conditions of grant spelled out by a funder. It’s not as easy (although it can be done) to make a case for something that seems as though it will attract funding, rather than starting with a plan for which funding can be identified. Munch is also right to say that you shouldn’t start writing until you know what questions you need to answer.
Good luck in finding funding.