i have the same muther bord and will run 4gig but 2 gig sticks of ram. you should of poot them in yelow slots and if xp 32 bit will only read at 3.50 but pc still usin 4 gig but that the maxs for that muther bord if was windos xp 64 bit will read as full 4 gig or mor. not best muther bord hafto say.
I've got the same problem with Asus P5KPL mobo. 3 sticks of ram. All pc 6400 DDR 2, CL5, 240 pin. One stick is a 2GB and the other two are 1 GB each. No matter which slot I use, it won't accept 4 GB without getting an alarm going off on the motherboard and it refuses to boot to bios. It works fine with any combination adding up to 3 GB. Yet the manual claims support for 4GB. Weird, huh?