Can someone please tell me whether BC2.1 update supports XP/Vista 64bit?

Hello

I've been reading/searching but I find no definitive answer. I'd like to know whether the new update of Boot Camp 2.1 supports native 64 bit vista/xp.

I don't mind using either XP or Vista, but there's three updates and I dunno which one to install.

There's three updates, called "XP", "Vista 32", and "Vista 64".

• If I install XP x64 SP3, does the new update support 64 bit?
• If I install Vista x64, does it support 64 bit?
• If I install Vista x86, does the "Vista 64" update support that?

The reason why I'm asking this is because I've got 4GB of RAM that came with my MacBook. So far Vista x86 is showing 3GB because it doesn't support more than three GB of RAM...