It depends on the game. For a full commercial release you would be looking at 2GB up to around 7GB. inFamous is just over 7GB so would eat into your 60GB HD space quite a bit.

It is really easy to swap your PS3 HD for a larger one though. 320GB 2.5" HDs can be purchased for around £35 these days, and using an external HD plugged into the PS3's USB ports you can select to backup the existing HD to the external drive, then swap the HDDs over and then copy the backups back over to the new drive. Not too hard.