Yep. Just bring down the VE and tar it to template/cache under a name which describes it. Under my Debian install I have:
strato:~# ls -l /var/lib/vz/template/cache/
total 61044
-rw-r--r-- 1 root root 30649140 Aug 5 22:49 debian-3.1-amd64-miniserver.tar.gz
-rw-r--r-- 1 root root 31780944 Aug 5 21:01 debian-3.1-i386-miniserver.tar.gz
So I can use:
strato:~#vzctl create <VEID> --ostemplate debian-3.1-amd64-miniserver --config bat_small
which gives me a 64 bits Debian minimal server with minimal resources (in /etc/vz/conf/ I have a ve-bat_small.conf-sample with my own settings as well). To make it realy Debian I packed both templates, which is handy if you have multiple servers to maintain
.