Dammit, stop posting in different sections.
Do you know what an AGP or PCI Express slot looks like?
If so grab yourself a 6800GT or equivalent, (look at THG gfx card tables) and your away, the rest of your machine is fine.
After that, I dunno, you probably will need to go into the bios and disable the onboard GFX, I think so you need to be comfortable with that stuff but others can give you better advice there.
As for comparable games, CoD1 is virtually out on it's own
CoD2 doesn't hold a candle to it in my eyes but is more of the same.
Personally once you get a better GFX card then download and try in no particular order:
Aliens Vs Predator 2
FEAR
COD1
Chronicles of Riddick: Escape from Butcher Bay
HL2 I suppose despite me hating it.
Hidden and Dangerous 2
No One Lives Forever 2
Battlefield 2
Can't think of any others off the top of my head but don't stop with just FPSs
Download
Rome Total War
Command and Conquer Generals
Nexus: The Jupiter Incident
Homeworld 1 and 2
RPG:
Baldurs Gate 2
Morrowind
Neverwinter Nights
Vampires the masquerade: Bloodlines
Flight sims:
IL2 Sturmovik and it's add on packs
Lock On
Space Sims:
Freelancer
X2: The Threat
X3: Reunion
Independence wars: Edge of Chaos
Ah crap, can't think of the best space games ever...... what was it called, something wars..... Argh! Someone help me out here game was you as a fighter pilot against these insect like aliens.... Their battleships were HUGE...... Oh my poor aging gamer brain can't remember.
Anyway I need to get back to work.