First let me say welcome to Linux and Slackware!
Second definatley switch to the 2.6 kernel, the wireless support is way better. Thats the first thing your going to want to do, second you need to see if there is a linux native driver for that card, I just checked the kernel and madwifi, they dont seem to support your card. I cant really walk you through because I have yet to setup one myself, however I would definatly checkout the networking forums, there probably going to be a better help. Just keep in mind though that its worth it, I've been using slack since 2000 and even after all that time I still run into problems every now and again, it took me 6 hours to get my widescreen LCD working correctly last week