"...would an internal adaptor card be much better?"
Quite probably, though not definitely. Your notebook's integral mini-PCI adapter is almost certainly more effective than a small USB adapter, though USBs are sometimes further handicapped by users who install the manufacturer's management software (they often erroneously believe that it is [a] just a driver and [b] necessary) which is typically less efficient than WZC. WZC can and should be used regardless of the format of the adapter.
A PCI card with aerial extension is more expensive than most other formats, but is usually a worthwhile investment. Double-check the encryption compatibility, which always used to be less certain than with USBs due to a higher number of older models in the marketplace -- that may have improved now.
Failing that, use a mains-carried Ethernet link via "Homeplugs". Look for the Dynamodes on Ebuyer, which are cheaper than most (particularly the over priced PCW offerings).