Buses and ferries and trains...oh my

[kari&amber]

I'm going to Britain (Scotland/England mostly) in May for about 3 weeks and I'm trying to sort out this 'getting around' thing. I was thinking of getting a 15 day britrail pass, but then someone told me that it is better to get a 'freedom of scotland' pass which allows use of ferry, rail and bus in Scotland but then I would have to get a seperate pass for England. So, my question is, are 'rail only' passes sufficient (how extensive are rail systems in Scotland) or should I look at passes with bus included? Also feel free to dispense general advice and knowledge (preferably about backpacking, but any other advice welcome ) Thanks!!