Building A New Computer - Input Pls!

OK my current PC is about 5 years old, my specs are :

AMD Athalon XP 2100+ 1.74GHz w/ 2.5 GB RAM
vid card is an NVidea GeForce 7600GS 256k

I'm tired of 8 - 12 hours+ to render a picture (and we're not talking bigger than maybe 1800x1800!) and there's no way I can use Bryce it just isn't viable to render from there (even if what I tried was worth it *snicker* ) Just running Daz|Studio for long periods of time has my system jerky and if I try to render and do anything else.. *hahahaha*

Here is the rough guidelines of what I want :

Intel 2.0+GHz dual core 4GB RAM
GeForce 8600 GT w/ 512k or possibly dual 8500 w/ 512k ea (dream is dual 8600 but would settle for one now on an SLI ready board so I can add later)

Will be running XP Pro SP2

I want to build a system that will last me another 5ish years give or take with some small upgrades (memory, vid card etc) Should I go quad proc? I thought I had heard there were problems with those and compatibility with Poser / Daz|Studio and other things, or is that just Vista and I'm confused? Also if I was to compromise on anything what should it be? I have a budget of aprox $600 for all this and I need new case and all the goodies so I was thinking a good barebones since I still have my HDs but that's about all since I'd like to leave my current machine as intact as possible for a "spare". I am willing to go 2GB memory now and upgrade as funds permit so that's a little wiggle room I think.

And if anyone knows of someplace to get a sexy red case, mid tower or smaller but no micros (and no room for a full tower) please let me know.

Thanks for any input or leads =)