Trouble need help pls !!!!

Hello, i just made a new comp couple of month ago and it was my first time started computer and everything seem running fine BUT when i play some game i get some glitch need to download coolbite and turn the v-sync always on also some game will run choppy. Game like UT 2003 will have glitch but perfo not too bad, battlefield 1942 choppy and glitch, morrowind choppy, warcraft 3 run ok with everything high, mafia run ok with everything high so am comfuse what going on with my comp proly something defect but not sure what. My cpu is P4 2,26 but actualy run at 2271mhz instead of 2260 nothing O/C, first i was thinking it was my vid card send email to store i buyed it guy told me it could be my memory that was bad i done some test i got over 11k in 3dmark and pcmark test seem good result done sandra all fine memory test was good so any advice would be great b4 i decide to buy some new memory or new vid card so i can send defect part back thx. Oh also my mobo is Gigabyte GA-8IHXP but at first when i ordered my part i ad a asus p4t533-c and return it cuz board was not detecting my ram. First when i started asus board i manage to make it run with bios update played game and i ad same trouble too so i decided to play with bios trying diff one after couple of reboot system crash and was not able to detect memory anymore so i returned it and get the gigabyte and the board detected my ram at start. Thx

Ok Battlefeild 1942 is Memory monster and will eat everything you give it aslo if you mess around with Enemy AI and amount of troops this will seriously affect your gaming performance you should start at the default settings and slowly work your way up as i guess you did what we all do and crank the lot to max to see how it runs some games you can do this but others you can't , also you might want to see what your case Temps are my GFX card tends to complain if my case is a tad warm so i keep well vented at all times but first i would try setting things at standard first and your memory realy isn't upto scratch for maxing out BF1942 i have over a gig and it still uses as much as possible!

Let me know how it works out!