I'm trying to install Xen hypervisor on our amd64 box with NetBSD-4.0. I'm getting a couple of errors on getting it to run. The friendly folks at #netbsd told me that I either need to use i386 kernel or use the bleeding edge NetBSD-CURRENT. They suggested that I setup a wiki page to document my progress. I've created an account at http://wiki.netbsd.se/ and I'll see how it goes. I hope this small contribution would benefit others who need to use Xen/NetBSD on x86_64 hardware.
UPDATE: Here's the wiki page-- http://wiki.netbsd.se/Xen_3.1_on_x86_64