im reading through old posts to see if i can help with unsolved mysteries, and i found this and thought it might be of use to you...
"(P.S. the reason the motherboard went F-U after i put in that 3rd memory chip was because, as i found out AFTER reading my mobo manual [yes, i know, rtfm], the 3rd memory slot in the P4B266 can only take single-sided DDR chips)"
the guy had 1gb of ram in his pc already, and put a 512mb in extra and got loads of BSODs etc.