"I need to find out what patches are/are not installed on my SuSE 7.0 mail server."
Red Hat patches are installed as rpm updates. You can use:
rpm -qa | sort | less
to find out what rpm packages are currently installed. rpm does not have a log function so you cannot find a list of what rpms were updated and when. To do this you would have to compare your rpm list to a list of recommended rpm updates.
I keep track up updates with my own personal system maintenance log. I suggest that you start keeping a system maintenance log.
Be prepared. Create a LifeBoat CD.