really choppy gameplay

I don't know if this is in regards to the motherboard but i am desperately hoping someone will be able to help. I have an odd problem, where I run games (even really old ones like cs 1.6) and the gameplay is choppy. Character models look static when they begin to move around. I get alot of choke when I shouldn't be... also when many different sounds are going on at once, some sounds will simply not be heard when I know they should be. When many people are on my screen, gameplay gets very sluggish. Finally, for example, when the bomb is planted and the sound of the bomb is ticking... u can hear the sound of the ticking actually glitching kinda like a hiccup. Finally, my fps in 1.6 begin to dip into the 90's and 80's when i bring up my console which with my rig should never even sniff under 100 constant with 30 guys on my screen.

Finally, i don't know if this little fact will help but, if I even try to overclock the CPU by adding 1mhz to the FSB my FPS ingame dont even touch 100.

I have the newest mobo/video/sound drivers available... I also have the windows multi-core fix. I have tried switching out video cards, sound cards (on board too), memory, cpu, psu, and HDD. I am at a loss, have no clue what I can possibly do. Was wondering if this was maybe a common problem or if someone else could give me some guidance in what direction to turn because I am very frustrated. I have been trying to fix this for months now.

Thanks in advance.

My Specs:

Intel Q6600
MSI P6N SLI Platinum
250Gig WD 16mb 7200rpm HDD
2gig (2x1gig) G.Skill DDR2 Ram
600W Thermaltake PSU
XFI-Xtreme Gamer Sound Card