Hi shonabby, You may have two wireless cards working in the computer at the same time. However, each one will be managed by its own software utility and one needs to be disabled from 'Device Manager' to get uninterrupted wireless connectivity through the other one. You may disable the onboard wireless adapter from 'Device Manager' by following the steps below: Once done, use the software installation CD to install the drivers/software for the USB adapter. Plug the wireless USB adapter when prompted and follow the onscreen instructions. Please reply for further clarifications. 
Since My 27 inch XPS ONE all in one has only a 2.4 WLAN, I am buying a dual channel usb adapter. Do I have to disable the internal card, and if you, do I do it before or after I install the usb wifi adapter?
WLAN and USB adapter Overcoming the XPS One Shortcoming