BYON 3311 Broadcom wireless driver for XP

http://support.us.dell.com/support/downloads/
download.aspx?c=us&l=en&s=gen&releaseid=R174291&
formatcnt=1&libid=0&fileid=236819

UPDATE April 8, 2011:
above link no longer exists
better lookup the device & download driver from http://devid.info/