Emulating different versions of FreeBSD

[Andreas Nilsson]

Hello,

I need do build packages for some different versions of FreeBSD ( 7.1, 7.2
and 8.0 ) and today I'm running a xen domU for each version, which is not
optimal for performance.

Could the jail architecture be used to run/emulate different versions of
FreeBSD on the same machine? My idea was to install a 8.0 and then have
three jails: one each for 7.1, 7.2 and 8.0, with the respective userland.
Can the kernel be tricked into telling a jail that it runs an older version
( i.e. 8.0 kernel tells jail it's running 7.1 )?

Best regards
Andreas