If the internal card has no MMCX, or other RF antenna connector the best thing you can do is get a USB hub and usb adapter, or PC cardbus (PC Express or PCMCIA) w/ an external rf connector. Oh yeah, you could get a new internal with an RF antenna jack too, but you'd more than likely need to mod the laptop chassis.
If you know how to solder you might be able to add an rf connector the the current internal card. However, you'd have to be both skilled and lucky (lucky because not all internals can be moded).
EDIT: you could look at the problem from outside the box, and put a better antenna and/or RF amplifier on the AP.
i just looked at your dell model and your best solution is a PCMCIA wifi card. Checkout Ubiquiti, they make some nice ones: http://cgi.ebay.com/UBIQUITI-SRC-WLAN-300mW-802-11-a-b-g-PCMCIA-CARD-NEW-/120559101888?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item1c11e1e7c0#ht_3213wt_939
that one is nice, I own one myself. It is also considered high-powered at 300mw and has dual MMC antenna jacks.