I have a PDA with Tom Tom installed and UK/ European maps. It is easy to switch between maps, you just need to make sure you have the most recent version possible, which is V6.something. Halfords and the like are selling the Tom Tom One with European mapping for £149.
As with all sat navs though, a certain amount of common sense is needed when using them. Some of the instructions aren't very clear, it will tell you to keep left when it means turn left. Other than that, they are a very handy bit of kit, and TT are currently stil the best out there for the money at the moment
Mark