[CentOS] looking for cool, post-install things to do on a centos 5.5 system

> >   over the next several weeks, i'm teaching some courses in 
> > RHEL admin but (unsurprisingly) i'll be using centos 5.5.  
> > it's a decently-written, 3rd party course, all the generic, 
> > standard admin topics but it does leave me about a 1/2 day 
> > to throw in any cool stuff i want to add.
> > so, any recommendations for neat things that people here 
> > have done 

For me: I'd want to have a closer look at things that *might* give
advantages but DO bring troubles:
SEL
KVM

And dangers such as
DoS
DDoS
Zombie computers randomly port-scanning
Internal user ignorance, apathy, malice, and mis-information about how
to secure the campus network from the hostile world.
A boss who does not understand what he wants, but he wants it real bad.
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