i have been trying to play a game on my dell

and the game is halo
the game minimum cpu speed is less than 800MHz and this ones is 3,000
the game still laggs all the time even with all of the other programs closed and i am thinking i have too many running processes .... i think i have about 40 normally running is this too many?
and how many need to be running for the game and the computer to run without any thing else?
any help aprecaited
