what kind of portable aerial are you using...the cheap'n'cheerful loop aerials that come with portables aren't really up to the job of recieving freeview to be honest...might be better getting a new one from Comet etc.
Also, check
here just to double check that you can indeed recieve freeview in the area you are in.
---------- Post added at 17:07 ---------- Previous post was at 17:05 ----------
oh, and you will need something like
this to connect the box to your TV - you will be able to pick a cheaper version that this one up from your local electronics store