Run games well?

My iMac specs:

newest alum imac, just got it about a week ago.
20"
2.0ghz
1gb ram
ATI Radeon HD2400 with 128mb VRAM(if anyone could clue me in as to what this is i'd love it)
and only iwork, ilife, and adium on it application wise.

Now, I'm not looking to run Crysis or anything major on here, just CSS or Halo 1, something to get me through a boring weekend(such as this). Would my current specs be able to handle a game like this?
I havent the smallest clue about any of the gaming specs and what is good vs. what is bad, so if anyone would like to give me an idiots guide to gaming hardware it would be appreciated.

AustinD said:

ATI Radeon HD2400 with 128mb VRAM(if anyone could clue me in as to what this is i'd love it)

Click to expand...

http://en.wikipedia.org/wiki/Dynamic_random_access_memory#Video_DRAM_.28VRAM.29

While it isnt actual "VRAM" on the video card, that has become somewhat of a standard term in referring dedicated memory for the video card. The card itself actually has GDDR3 memory

http://en.wikipedia.org/wiki/GDDR3