There are several ways to Enumerate (check your spelling) an OS. Since you already know it is Red Hat 7.3 you can check out Bugtraq and know exactly what to look for. Founstones' Hacking Exposed (TM) books devote entire chapters to tools and usage for enumeration. Although that shouldn't be necessary since it is your box and you know the OS and presumably what services are running.

However, for a simple Pentest just use nessus:

http://www.nessus.org/

It will do it all for you and give you tips on how to fix it.