i got doom 3 for 20 bucks and it really sucks

so slow on my poor computer...slow and jerky...i guess my 5200 vid card is just a not good enough,...

if feel so inadequate...maybe i just need more ram...

What are your system specs?

I'm assuming 5200 refers to a GeForce 5200? If so, yeah, you'll experience problems and won't be able to use quality graphics settings, but there are things you can do, depending on your system specs overall. I assume you've already set everything to the lowest settings, turned off any running services like a virus checker, firewall, etc. you don't need while playing. Get it as bare as possible to free up as much memory and resources as possible.

DOOM is a huge memory hog, so more memory might help. Playing it on a machine with less than a 1gig is going to result in jerkiness when doors open or any other sudden event takes place even if you have a more modern graphics card.

It's been awhile since I've played and have un-installed it from my system, which means I don't remember exactly how to do this. BUT, try googling something like "DOOM3 tweak guide" and see what turns up. Eventually you will find a guide to tweaking your config file settings based on your system specs. I know someone who, just for giggles, got DOOM3 working on a Pentium III class machine with an ATI Radeon 7500 and 128 megs of memory. It looked horrible, sort of like crayon drawings, but it worked and was smooth.

BTW, don't expend too many dollars trying to get it to work well if that's the only reason you're doing it. It's an interesting diversion if you like the game series on which it is based, but overall, it bored me. Once you "figure it out," it doesn't require much more than the patience to get to the end.