vista won't install or boot with more then 3gb ram

Why won't vista install or boot with more then 3gb ram?

my brother in law has 4 gb ram. It starts with a G I think. Intel E6600 dual
core. asus p5n32-sli-e motherboard.

vista home premium. also another person posted the same hardware cept didn't
say what board he has. he had ultimate vista. same problem.

when installing vista it won't get past the scrolling bar from the boot dvd.
it bsod. both people get same error. the ram is good too. you boot from dvd.
then it starts to show you the scrolling bAR WHILE IT TRIES TO LOAD the boot
dvd. it bsod everytime with all 4gb in the pc. take out one stick of ram for
4gb it works fine. put in stick of ram to make it 4gb after it is installed
and it won't boot up at all. take ram out for 3gb only and it works fine.
all ram is 100% good.