Using Ubuntu 64 bit server

[Larry Alkoff]

I'm reposting my original message stopped by the moderator because I 
have joined ubuntu-users of which I apparently was not a user.  Now I am.

I plan to purchase a 64 bit motherboard and memory
to run as a server under Ubuntu 64 bit AMD (includes Intel) server
10.04.1.  The memory is 16 gigabytes.

The same motherboard will run various OS under KVM virtualization including:

Ubuntu Desktop 32 or 64 bit version
Windows XP
Windows 7
Apple OS X (possibly)

My questions are:
1.  Will either 32 bit or 64 bit Ubuntu work well?
	Which is recommended?

2.  Will other 32 bit OS like XP work?

3.  How does the 64 bit server handle 32 bit code?
	If by thunking, is there any speed degradation?

Thanks,
Larry Alkoff