There shouldn't be any reason why your laptop can't have features added - it would be a very shortminded company to deny it's users new tech like this!
If you have a PCMCIA or PC Card slot (same thing) you can add a wireless adaptor to this:-
Or if don't have one of those you can get USB :-
What the documentation may have meant is that you can't have ONBOARD wireless added afterwards (i.e. built in to the computer).
Hope this is of some use