Wow 3 bumps in the matter of 10 minutes. No patience?
Your system sucks. You have 1 GB of RAM when it is recommended to run at LEAST 2GB for Ultimate. If nto more. So yeah that would be your first issue.
I have run F.E.A.R. with Full EVERYTHING and i still get 60+ FPS in Ultimate. So games run jsut fine on Ultiamte. Doom 3..same thing. Full everything with high details and yet 60+ FPS on each game. CS:S i get mroe than that with high detail.
Get more RAM. I run 3GB and my system runs smoothly. Even before my upgrade when i had 1/5GB of RAM, which is still higher than yours, i could run most games at high detials and still get 30+ FPS.