I recently installed a Linksys Wireless-N Notebook Adapter w/Dual-Band (WPC600N), which is working nicely via the PCMCIA slot; however, I cannot find where to permanently disable the internal WiFi adapter. Currently, I'm forced to manually disable it with each reboot.
Unless there is a hardware switch to turn it off, just blacklist the module.
You can find out which module is in use with this:
...to blacklist a module, add