Doing about the same thing for my cousin (as soon as he decides to actually start saving some money

)
I don't know how much digital art tasks the hard drive, but it might be worth it to splurge a little on the hard drive and maybe get either a Western Digital 80GB or 120GB Special Edition. The speed they provide may be worth the extra money. The 120GB version, WD1200JB at
NewEgg, costs $166; the 80GB version, WD800JB at
NewEgg, costs $107. Might be worth it, might not. Possibly a little digging around on these forums/The Net may yield the answer if a faster hard drive helps in digital editing - I don't know.
Also, from reading a bunch of forums, it seems like the nForce platform from nVidia seems to be very stable. Like I said before, I don't really know anything about digital editing, but I think it would suck to be working on something and have the computer crash. Asus's A7N266-C can be had for $105 right now at
NewEgg. It would also save you the cost of a sound card, since it already has very good onboard sound (widely regarded as somewhere in between a Live! and an Audigy).
It doesn't sound like you're going to be doing work full time. Perhaps a little less CPU could save you some money. Maybe a 1800+ or 1900+ CPU would be better. Then again, maybe not. It might be better to have all the CPU you can get and have a slow hard drive for what your doing. Maybe this is something you need to look at, i.e. research.
Memory: Two sticks of
Mushkin 256MB Hi Perf PC2100 DDR SDRAM 222 are $79 each right now. I think that's a pretty good deal, but then I'm biased towards Mushkin.
Just some more options for you...
Hope this helps!
Chuck