hi, i do some cad and a lot of dcc work and i think i can help you out.
i was in the same boat a couple of months ago and was looking for a killer machine to work revit.
the things i learned after buying a $2000 top of the line video card was that the "workstation" cards have some of the worst bang for the buck. You would be better off purchasing a "gaming" card and using that. for instance the fx560 costs about $250 and its based on a much cheaper nvidia chipset. so what you can do is (and what i have done) is to buy a gaming card for the same or even lower price. the Cpu i would strongly recommend getting an Intel conroe based cpu, they are the best on the market right now and the new opterons dont compete.
here is what i would buy (based on a budget of about $1500-$1700):
OPTICAL SAMSUNG 18X
CASE LIAN LI MID TOWER
HD SEAGATE 250 GB 7200RPM SATA 3.0
MONITOR SAMSUNG 20" 1680x1050
GPU BFG 7950GT 512MB
PSU ANTEC 500 WATT
KEBOARD + MOUSE LOGITECH (BASIC)
RAM OCZ 2GB 4-5-4-15 DDR2800
MOBO ASUS P5N-SLI 650i NVIDIA CHIPSET
CPU INEL XEON CONROE 3050 2.13GHZ
OS XP PRO SP2 W/ VISTA COUPON
TOTAL _____________________________ $1610
I personally feel that with the above computer you would be just fine through college. It has an amazing video card, reliable power supply, overclockable and stable cpu and motherboard, big monitor (the more room you have the faster you'll work in cad and dcc applicaitons).
also every thing is compatible with quad-core cpus so if you ever felt that you need to upgrade, it would be pretty easy (not that i foresee any need for upgrading in this comp.) the only thing is that the video card is dx9 and dx10 is coming up, the only cadd/dcc related program that would make use of this right away is 3dstudio max, so if you plan on using that and can stretch your budget to about $1750 you could have a completely future proof machine.
i hope this helps and PLEASE consider what i have listed here and let me know if you have any questions.