might have to troubleshoot the drivers to make it compatible
what wireless card is it?
boot the live cd in a cmd shell type "iwconfig"
does the wireless card show up there.. might read wifi0 / wlan0 but not the eth0 or the local one
just going into the k menu
select internet and then wireless assistant, can you use your wireless then?
just a pointer backtrack 3 is a live security pentesting suite which basically means its full of tools to test computer and network security
as an operating system its likely to not fulfill your needs as you say your switching from windows
just explore with the live cd for now and maybe have a look at dual-boot to really get the experience
in my opinion if your moving from windows xp i would aim for ubuntu 9.04 instead of backtrack
email me if you have any other questions about backtrack 3, i would be more than happy to answer them for you