Backtrack would be a good distro to load to access quite a few different tools.

http://www.remote-exploit.org/backtrack.html

No, but I'm definitely going to check it out. Thanks for bringing that up!

Mambo, you may want to look into a book called "Build Your Own Security Lab: A Field Guide for Network Testing". A friend of mine read it and he said it'd be a good start for people wanting to set up their own labs.

Alternatively you can check out NETinVM

NETinVM is a single VMware virtual machine image that contains, ready to run, a series of User-mode Linux (UML) virtual machines which, when started, conform a whole computer network inside the VMware virtual machine. Hence the name NETinVM, an acronym for NETwork in Virtual Machine. NETinVM has been conceived mainly as an educational tool for teaching and learning about operating systems, computer networks and system and network security, but other uses are certainly possible.

The thing with pentesting, is that you need SOMETHING to assess whether it's a service or network.  What I mean for service is whether it's a web server, database server, data center, web services, or even an IP voice solution.  By assessing the network, I mean attempting to assess targets through a real switch, real router, and multiple other security controls.

Hence my point is that you'll need to either team up with someone who knows how to configure servers, or a network guy unless you want to learn either one (or both!).  Not knowing how to do one at least leaves you at a major disadvantage I feel.

Great idea. You could get additional experience and knowledge by setting up additional linux VMs as IPS, Firewall, or for routing. This would teach you how to configure them, and how to get past them. Again, I recommend VMWare's ESXi since it is free and based on the industry leading VM platform. Not a bad idea to learn VMWare while you are at it. ESXi will allow you to set up multiple networks for setting up the lab described above.