CPU, drive speed, bus speed are the biggies, but there are a few things tossed into the mix.
Network rendering is used by several of us, I think. It's not worth it for small projects/short projects, IMO.

Anything can be a bottleneck (if you had a 128K RAM system, for instance), but having made that disclaimer, in most cases it is almost entirely the CPU: Double the CPU power, halve the render time.

yep =- cpu is most important

you dont even need a graphic card for rendering (in vegas that is , some application now use the graphics car also for rendering - like the nvidia plug in for maya and renderman and some other applications)

Yes, with Vegas is all cpu crunching. Also a big difference is made when you have physically separate drives. Optimally:
1. System
2. working or source material
3. Render drive

well i have a 1.4 ghz

i have a intel d850gb mobo and i think the highest you can upgrade to on it is a 2.0 ghz

so I might just have to get another cpu mobo combo....wanna stick with intel and p4 cuz i dont wanna have to buy new ram to.

that's a little down the road. i just bought a 200GB western digital and a nvideo 256 meg agp..with s-video and dvi capabilties

i plan on gettin an s-video capabilities so i can preview it on the tv. I'm slowly but surely building a video studio :)

Intel has nothing to do with the ram (unless it's RDram, which i don't think is used much anymore anyway, it's all DDR. The ram mostly depends on FSB too: 133fpb needs 266 (133x2) DDR, etc. So, if you bought a P4-3.0ghz MB you'd need new ram anyways). But, the S-Video won't give you output preview. You need a firewire to analog converter to do that (I think someone, somewhere said that you can have NVidia preview via s-vid from Vegas, but not sure).