I've got a Computer Music (I think?) special on Reason 4, which cost £7.99. Seems quite comprehensive, and I'm also using the ASK tutorial DVDs.
I had Sound Clart send me a sample project from Reason 3, but opening it in version 4.0 sees it asking me "where is xyz?" etc. I'm guessing I just need to point it in the right direction, rather than it being incompatible, right?
The things it was asking for are instruments/components of both. Just a bit annoying as I can't quite navigate it and say "check here", but I'll have another go later.