If you want to check which version of Ubuntu is installed on a machine run the following command:
lsb_release -a
On Debian the command is:
cat /etc/debian_version
The redhat equivalent, which would work on redhat derivatives as well, is:
cat /etc/redhat-release
em, lsb_release -a will work on Debian Etch, Centos 4+ and RHEL 4+ 🙂 Make life easier for yourself and just learn the one!!