The thing to remember with digital TV reception is that it has nothing to do with the analogue reception. You could have perfect analogue and still get nothing with Freeview, and the other way around. My analogue reception is next to unwatchable, but I get fairly good reception on Freeview from a loft aerial.
If you want to connect a Freeview box to a PC TV card via rf then you will need to check the specs of the Freeview box carefully as most of these boxes will only decode and output the Freeview signal via the scart sockets. The rf output will only pass through the analogue signal received from the aerial and not the decoded digital signal.
If you add a Freeview decoder to the PC via an internal PCI card or external USB box then the PQ on the PC will be far better as rf is the lowest quality connection going, even lower than composite! If you are going to buy a Freeview box anyway then this would be the best way to go as long as the PC is the only thing you want to plug it in to.
Mark.