Wireless networking isn't easy in Linux unfortunately. I've been trying to do this, and I managed it without the encryption, but I can't set an encryption key or anything. I know it's possible, but I also am very new to Linux and have found it very difficult.
The way I did it was, I went to
http://ndiswrapper.sourceforge.net/ and downloaded Ndiswrapper. This program uses your Windows XP drivers to make the card work in Linux. You also need to have Wirelsss Tools installed, this may already be on the system. If not, the package is available for download somewhere.
It will not be easy to set up, I have not yet properly set it up, but the best thing you can do for the moment is to read the beginners tutorialson
www.linux.org. This helped me rather a lot.
You can also go to
www.linuxquestions.org and read the forums there. There is a forum specifically for wireless networking, which is very useful.
Good luck anyway.