Hello,
Getting experience in a lab is a good idea. If you use real machines or virtual ones has very little impact on most attack scenarios. Of course, if you want to identify weaknesses in virtual systems, you have to setup such an environment. And there is some rare kind of behavior which only affects real machines (e.g. some 3d hardware isn't supported by some virtual solutions).
I was working within a lab with real machines for about 10 years. We've then switched to an environment consisting of approx 90% virtual machines (VMware-/ESX-based). It introduces some real advantages, which pay off in the end: Easy access to "exotic" systems[1], quicker backup/restore, multi-use of the same hardware (cheaper). I'd say, as long as you don't require real hardware for your testing, I'd stick with virtual machines. Have fun!
Regards,
Marc
PS: Most of our customers in financial services set-up most of their machines as virtual ones. Therefore testing in virtual environments isn't that way off of reality.
[1] Check pre-installed VMs at http://www.vmware.com/appliances/
