I have the same problem:
intel core 2 Duo, 2GHz, 3GB DDR 2
intel GMA 4500 MHD
using vista :
slow
but the funny stuff is:
my old computer
some celeron i think, 1GB DDR 2
intel GMA 950
using xp :
smooth and sometimes fast
I think the problem is the explosive combination with intel onboard cards and windows vista
EDIT: Your CPU is too slow to run Vista anyways, unistaling vista and installing xp migth solve the problem