counterstrike: source lags/freezes heres my setup

here are my specs:

amd x64 3200
2 512 corsair ddr ram
ati radeon x1900 pci express
asus a8r32 mvp deluxe motherboard
2 fans
another fan on top of cpu
500 watt power supply



just made my system up the other day; updated all the directx and .net microsoft updates. when i do the video stress test there are lags/freezes; also when i play cs:s.
it freezes for abt 15 seconds every 7 seconds. can anyone help me? thanks in advance... i was wondering i am using 2 seperate old hard drives abt 4-6 years old. i did the whole defragmenting and errorchecking still same problems. i was wondering can it be my hard drive can be too slow. what can i do?