Question about using both an internal network card and an external network adapter

Hi there,

I just got a new XPS 1530 laptop which I love.  It comes with an internal WLAN card.  The router for our wireless is in my landlord's house which is only about 50 feet away.  She has AT&T internet service, the only service we can get in the area we are in.  They sold her the product telling her that anyone within 20 bus lengths would get an excellent signal.  They failed to tell her that the material that her house is made out of is muffling the signal.  For me, the signal is so poor that I either can't connect to the network or, if I do, it is constant disconnect and slow to the point of screaming.

 My very old Dell Dimension desktop has a link-sys external antenna and I can access the network fine on that - it has a "good" signal strength compared with "poor" on my laptop.

So I ordered a WUSB600N Ultra RangePlus Dual-Band Wireless-N USB Network Adapter for my laptop to help boost the signal.  The question is - do both the internal WLAN card and the external antenna work together?  Or do I need to disable the internal one before the external one will work. 

Thanks much!

Roxanne