upgrading from netbsd 4/xen 3.1 on i386 to HEAD on amd64

["Chris Brookes" <cbrookes%gmail.com@localhost>]

I'm currently running NetBSD 4/Xen 3.1 on a 1.0Ghz i386 box for DOM0.
I have a few NetBSD 4 DOMU's  and a single Linux (Ubuntu 7.10) DOMU.
I've got an Athlon X2 BE-2350 and a GIGABYTE GA-MA69VM-S2 mobo on the
way which I'm hoping to run the NetBSD HEAD/current amd64 port on for
Dom-0. Will I be able to boot and run my existing PV 32bit DOMU NetBSD
and Linux installations while running under the amd64 DOM0?  If so
what kernels do I use, my existing ones? This will greatly aide my
upgrade path to 64 bits for the DOMUs...

How mature is HVM support with NetBSD and xen? Am I likely to run in
to much trouble getting an XP or MS Server 2003 instance running?

Cheers
CB