lately my pc's been acting up. it freezes for about 15 seconds then its fine again. usually it happens every minute.. and its really really annoying. sometimes when i play games and i have to fight monsters, the comp freezes and fifteen seconds later i'm dead

i can still hear the audio though, and when it freezes i can still move the mouse pointer. but i cant click or do anything... i noticed that the freezes usually happen when i do something significant, for example, when i'm playing NBA live, and the player goes to the hoop for a lay-up, the comp freezes right before the foul animation..
or sometimes when i'm browsing the net, it freezes right after i click "new tab"

i have searched google but found nothing relating to my problem.. i am pretty sure it is a hardware problem, because sometimes, i open up the computer and clean the insides. but i dont ground myself (because i dont know how to).

specs are:

pentium 4 XP
512 mb ram
128 mb Geforce 5 video card
2.2 ghz processor speed

so i have now given the most accurate description i could give, so please somebody help me!

plus, i really dont know of the proper forum to post this. so move if necessary