If your signal is that weak, I'd suggest getting one of these aerials:
http://www.screwfix.com/prods/60215/...h-Gain-Digital
I'll be getting one to put on the roof at home, as we're on the edge of the Tacolneston transmitter, and cannot get 5 on analogue, and the Freeview is not the best it could be. I know this'll improve when analogue gets switched off, but 3 years is a long time.