I jsut got the majority of my computer parts, and I've had no luck getting the thing to boot up. I've got all the power supplies available where they belong, according to the book that came with my mobo. It's getting power, because the LED on the board lights up, as well as the onboard NIC, so I don't think it's a faulty power supply, but I could be wrong because the fans don't come on(case or processor). I noticed that the ram I ordered isn't on the 'tested and working' list that was also provided with the mobo, so I was thinking that might be the problem, but I really don't know. I'm going to re-read the book again in the morning, but I need to sleep now, as I've been working on this all day pretty much.
Any help is appreciated, here's the stuff I bought..

MB ASUS P4S800 SIS 648FX RET
CPU P4/2.8CGHz 800M 478P/512K HT RT
DDRAM 512MB|64X64 VS DDR400 COR
*CDRW/DVD COMBO SONY CRX300E/A
CASE LITE ON|MT950 300W USB BK RTL

newer video card coming soon, using a geforce 4 mx420 at the moment.

I would not try to boot that up with a 300W PSU, there are very few that will, first thing i do with a case that has a 300W PSU is throw it in the bin, with todays technology i do not know why they bother installing them.The motherboard LED stays on wether system is booted up or not.
Get a good PSU. Antec 430W, or a Enermax 460W. I would not be concerned about the RAM qualified vendor list, see what it is like when it boots up, you may only have problems with cheap shoddy memory

Okay, off to buy a new power supply, I'm hoping that's the only problem. Thanks for the advice

Friend fixed it.. had a couple thigns reversed.