What is the stock card? How old is this HP Pavilion? I don't see any references to a stock card on the HP site, or a wireless socket.
Looks as if you will have to install a PCMCIA wireless card. Easy enough, and low in cost.
Most brands work fine. Nearly every electronics computer store, and of course on eBay... I recommend those by Verizon or DLink... simply because of the universality of drivers.