Make sure you set-up your firewalls as instructed here: http://www.limewire.com/english/content/firewalls.shtml for XP & McAffee link can be found at bottom of that page.
So your modem is probably a Broadcom softw modem that's packaged in Dell computers. This is a link to their modems & softw drivers: http://www.modemsite.com/56k/bcm.asp