Im not able to tell what kind of onboard nic you have the dell website is not very descriptive but you do have the Intel 2200b/g wifi card. Instead of the ndiswrapper try the ipw2200 driver, this is what I use on Slackware with this wifi card and it works like a champ for browsing the web, gaming etc, no working rfmon or injection from this card though atm
http://ipw2200.sourceforge.net/