Well I am a computer builder myself (building so far around 15 computers). To run 3D apps. there is not much to it. Here are the basics that you should need. These are my recommended settings that you should do, believe me because I have run into these things with my own system.
-AMD 3.2GHz dual core or quad core. The dual will only run you around $80 where the quad will run you around $120.
-2GB DDR3 Ram. This will give you plenty if you are running Windows XP, if you are running Windows 7 or Vista then you should probably get 4GB. 2GB will run you around $80 where 4GB will be around $160.
-The motherboard needs to match the CPU socket type. For most AMD quad-cores they will be AM2+ or AM3. They need to line up or it will not work. Make sure it has 4 slots for RAM, a PCI-E 2.0 slot, a few SATA 3GB/S connectors. This should only be around $80-$120.
-The case should have a nice 500 Watt power supply. You also need to make sure the case fits the architecture of your motherboard. Should only run you around $50-$70.
-Get a 320GB or 500GB hard drive. Make sure it is SATA 3GB/S connector. This will only be around $50-$70.
-Get a nice DVD-RW drive that is SATA 3GB/S connector. Only around $30-$50.
-The final piece is the Graphics card. I am personally an ATI fan so I will direct you on those. Go with a HD5750 or a HD5770. Both of these graphic cards will only run you around $150-$200 and they will keep up with the graphics for around 4 to 6 years from now which is great for graphic cards.
This should be the system that you are looking for. The places to buy the parts would be
www.newegg.com. They have an amazing selection and their prices are outstanding. If you have any other questions just shoot me an email or just send me a private message on here. I am happy to help at anytime.