As far as gfx cards go - you have a PCIe x16 slot? If you do just get a low-end gfx card or upgrade your whole PC a bit and get a mid-end card.
Examples of cheap low-end cards would be something like the ATI 5550 (around $65 or something) or maybe even the ATI 5670.
Example 5550 - XFX HD555XZNF2 Radeon HD 5550 Video Card - 1024MB GDDR2, PCI-Express 2.0, DVI, VGA, HDMI at TigerDirect.com
Example 5670 - HIS H567Q512 Radeon HD 5670 Video Card - 512MB DDR5, PCI-Express 2.0, CrossFireX, DVI, VGA, HDMI at TigerDirect.com
You probably wouldn't need a PSU upgrade for either, the max the 5670 can do is around 80W without overclocking, the 5550 draws only 50W or something. Personally I would try to get the 5670, it's pretty decent for that price.
If you want better suggestions try to give complete PC specs.