Hi,
Aside from the known issues with newer Ubuntu kernels not working on
the Xen hypervisor from Debian Lenny (which is what BitFolk uses),
there also appears to be a lack of compatibility between newer
releases of Ubuntu and older kernels:
https://bugs.launchpad.net/ubuntu/+source/mountall/+bug/447747
This will leave you in the position of not being able to boot with
the supplied kernel and not being able to revert to a kernel from
Hardy or Lenny.
There may be a workaround, I'm not sure yet, but at the moment I
wouldn't recommend trying to do this unless you know you can make it
work (or know you can fix it from the rescue env.).
Cheers,
Andy
--
http://bitfolk.com/ -- No-nonsense VPS hosting
"I'd be happy to buy all variations of sex to ensure I got what I wanted."
-- Gary Coates (talking about cabling)