Now is a very good time to get a very fast and cheap computer. AMD dual cores are at their lowest Prices ever. Think X2 5200. You can also get a DX 10 compatible card for a nice price too, Like the Geforce 8600. That said DX 9 is still useful and the 7000 series of cards are a very good price. 2 gigs of good DDR2 ram is now also only 100 dollars.
I bought a very capable computer a year ago the processor, 400 bones, Graphics card $350, and RAM $300. Today the prices are 60$, 100$, 100$ respectively for the same gear. Damn!