What is the hard drive? A SSD or hybrid can make a huge difference in how fast the PC boots and how fast applications start, and that is the only situation where many users really notice slowness.
I’d seriously compare costs of upgrading vs replacing with new; past a certain point, it’s more expensive to upgrade an existing system than it would end up being to replace the motherboard, CPU and memory to a middle-of-the-road modern system. And on top of that, the new system will likely have more performance.
For example, DDR3 memory is both cheaper and faster than DDR2 these days. That said, I think more and faster RAM is the biggest bang for your buck, along with replacing that ancient-ass video card, assuming your Dad does anything that taxes a video card. That processor’s still decently powerful however. I might get a better cooler and try overclocking it.
You can upgrade that Q6600 to a 3.0 GHz quad-core for 0 dollars. Check out the “pad mod” or “pin mod” for the Q6600. I did it on my Dell system, and ran it for half a year with no problems at all. After that I decided I wanted to save a bit of energy and took off the tape.
Meh. Pin-mod all the way. $0. 
I agree with this. Upgrading really only makes sense for last-gen computers that need a tweak or two. Once you get past $200 in upgrades, you might as well buy a new machine that will be in warranty and give you a new starting point. I’m amazed that the OP’s machine can even run Win 8 on 2gb of RAM.
Thanks for the advice everyone. Upgrading cost less than 400 and ended up getting new ram, graphics card, cpu and ssd. It’ll be like a new computer when I’m done with it and it’ll be way less of a hassle than buying a new pc and transferring everything over.
Cool. 
Happy Holidays!
Because you’re using a SSD, you should reinstall Windows rather than clone the drive. This is because Windows will then know it’s booting from a SSD and enable SSD support and disable defragmentation.
Don’t be surprised if Windows fails to activate due to so many hardware changes. Just follow the instructions and ring Microsoft and they’ll sort you out.
Also ABSOLUTELY make sure that if you have a swap file in Windows, that it’s NOT on your SSD.
The way SSDs work, they have a finite number of writes that can be done to them, but unlimited reads. Swap files tend to read and write a lot to the disk, especially if you’re using a lot of virtual memory, and that’s a terrible idea with a SSD.
Sad Update: The graphics card, SSD and ram were ordered through Amazon by 2nd day air. UPS did not deliver them on the 24th. I called and was told there was a network glitch and that the package would arrive on the 26th. I checked again tonight a few minutes ago and the scheduled delivery according to UPS was the 27th, the day I fly out of Oregon and back to Houston. These parts will be useless to my father because he would not be able to install it and test it all out, work out driver issues, reinstall windows, etc, on his own, and they would just sit around or he’d have to have an expert paid to do it all for him (and I don’t trust them anyway in this one horse town he lives in).
So I called Amazon again, just got off the phone with them, and they said that there was no way it was getting here on the 26th, and so they offered to send a recall and cancel the order, which is what I did.
The only part that was sent successfully was that CPU bought off of ebay that went through USPS. I installed it today and stress tested it for a while and it’s working quite well, was recognized in my BIOS and by windows and should be a nice upgrade for him.
He really needs more RAM though so it’s a shame he’ll have to make due with what he has until I’m back in town and can try it again.
I’m a little annoyed with Amazon because for 4 days they did nothing, until I called them, when they gauranteed it would be here on the 26th, only to find out that no, it won’t be here until the 27th. But I should probably be more annoyed with UPS, who I have always hated with a burning passion.