Here's a few things I'd recommend from my experience:
Read the Hacking Exposed books
Buy a copy of VMware Workstation, or just download VMware server if you can't afford it. Setup a lab, install and try every OS you can get your hands on, run pen testing and vulnerability assessment tools against them. You'll likely be using VMware on the job as well. From experience I recommend running it under Windows, simply for the effortless hardware support (it'll save you time, trust me)
Throw out any major OS bias if you have one. OS zealotry will get you nowhere in this field...you better know Windows just as well as Linux, because you'll be seeing it a lot. It's not too hard to stay sharp on both though, since you'll be running most of the tools from Linux
Start studying the CISSP CBK, even if you're a ways off from taking the test. It's a very good foundation of knowledge for security and gives you a good idea of the business aspects of it as well.
Last edited by JeffCT
on Mon Oct 15, 2007 8:13 pm, edited 1 time in total.