Look for IRQ conflicts, they can cause lockups.

Also, is there any specific behaviour (like while surfing the net and/or listening to music...or playing 3d games) that these lockups occur or is it completely random?

------------------
ASUS A7V + 1.4ghz Athlon t-bird ,Swiftech MC462a, 512mb (generic) pc133 @143mhz(2-2-2), IBM 75GXP, ASUS Geforce2 GTS, SB-Live5.1,12x10x32 Plexwriter,16x40x Pioneer DVD, Cable, Win98SE