this isn't perfect, or complete, but there is a minimal 64-bit and/or 386/pae usb boot environment here http://ftp.quanstro.net/other/usbtest.bz2. it's only 10mb, so it should be a quick download. the reason for building this was to quickly debug a system that wouldn't install, but it might be interesting to try out.
a few random notes and gotchas: 0. with dhcp, one can get to get to the full distribution with: ip/ipconfig && ndb/dns && 9fs atom 1. you will find the usb boot device @ /dev/sdu0, a loopback device. 2. there is a bug in kfs (patched in 9atom; patch submitted to sources) to be aware of. so be careful if using tools from sources on 64-bit kernels. 3. finally, there's (by plan 9 standards) quite a bit of acpi support in the 64-bit kernel. power events have been somewhat rashly turned on, and may cause trouble. as always, i'd be interested in any reports of success or failure. - erik