Dell has some _very_ nice service manuals on their website for the majority of their computers.
Here is yours:
http://support.dell.com/support/edocs/s ... /index.htm
It looks like there's a miniPCI slot, with which you can install a wireless card, although you may need to get creative in terms of installing the antenna wires... most laptops have a wire connected to the card that goes to the back of the monitor to give it some height.
You could also skip all this and just get a PCMCIA or USB wifi card.