Reference your Users Guide or Service Manual linked here (Support tab above-Users Guides) for specific instructions on installing or replacing the internal mini PCI card.

 

http://support.dell.com/support/edocs/systems/latc640/en/index.htm

 

Antennas are built in on most of the notebooks even if not sold with a card. Most any mini PCI should work, check out Dell sales, notebook accessoriesperipherals.

 

http://www1.us.dell.com/content/topics/global.aspx/solutions/en/truemobile?c=us&cs=04&l=en&s=bsd&~tab=4

 

Any number of Card adapters are out there, some folks like these better because they can easily change them, swap 'em around if travelling etc.