Well considering yeh only have 3 gigs of memory and tried to go to dalaran...

Try going with only yer main and one other do ctrl alt delete and see how much memory both take.

Most likely what happen is all yer wow's ballooned up to more then yeh have memory Xp started dropping thing to the hard drive at the same time its trying to load texture to the graphics card while trying update the screen of a wow that got dropped to the harddrive lots of thrashing occured till finally something gave out.

having separate instalsl of wow will make this worse.