MACs and PCs both use the industry standard TCP-IP which would standardize the packets. I had a problem similar at a school district a few years ago. The software did not work for me either, however a simple fix was just to use the built in system on winxp. I do now know vista very well, so I can only hope it is the same for vista. Open the built in program that detects a wireless network, Wireless network connections (NOT one that HP, or DELL install with their own software), when connecting you should enter the WEP key if it is a secure connection. It took a few tries but finally it started talking, in my case.
Keep in mind this may have only worked with the router I was connecting too. I wish you luck! (never liked the problems between mac and pc hardware and software....and I am a PC guru over MAC)