For those of you that don't know what nessus is or maybe you've heard of it but maybe havent put any time into gathering info on it, it is THE best vulnerbility scanner in my opion, and I will tell you why:
1)You can review the source-code of the main tool and any of the security checks to look for dangerous functions

2)A large group of developers are involved in seeing at its success

3)It is free

4)You can write your ver own vulnerbility checks and incorporate them into the scanner

And it is this last reason that I post this thread, for those of you wishing to learn the architecture behind this great program and write your own scripts. Here it is http://www.nessus.org/doc/nasl.html
I suggest for any of you that are serious about getting into security that you take the time to learn about this program, hope this helps someone.Take it easy people.