If you got money to burn, think about an Adaptec SCSI controller and a few big HD’s. The digital imaging takes up a lot of space, and you will want a quick access/seek time on your hard drives.
Also make sure you get a firewire port and motherboard with USB 2.0. These will ensure that you can connect an external video source and transfer the data quickly to your hard drives.
The Video card is very important. Again, depending on your budget you will want to go as expensive as you can manage. If you got big bucks shoot for the ATI 9700 All-in-Wonder Pro. It had a built in TV tuner, input/output jacks for video and a lot of horsepower.
Memory - Lots.
Software - I’m not a pro, but in my limited experience you can’t go wrong with the Adobe series. Adobe Photoshop for photos and Adobe Premier for the video. They cost a few bills though…
I recommend Dell to most people these days for both business and home use. Just tell the guy what you want to do with it and they’ll get you the right machine. They do use the hard sell a little too much though, don’t let him talk you into stuff you don’t need.
Have you considered buying a Macintosh? I strikes me that the areas you are interested in, music, video production and photo editing, have long been considered the platforms strong points.
The free applications iTunes and iMovie are great for entry-level music and video editing respectively, while Apple’s Emmy award winning Final Cut software is widely considered one of, if not the, best nonlinear video editing applications available. Also, Adobe Photoshop is a Macintosh mainstay and can handle any photo editing task you throw at it. You could even run the free Linux editor the GIMP on Mac OS X with the new X11 app that Apple released.
Plus, all Macs come with equipped with FireWire, the standard for digital video, and the only way to connect an iPod (my personal favorite mp3 player).
Now, obviously if you have already invested a fortune into windows software, or need to play all of the latest video games the day they come out, you should probably stick to a windows system. However, for the areas that you are interested in, I would strongly suggest looking into a Macintosh.
If you do get an apple computer a dual processor power mac will probably be best for video editing and photo manipulation.