Well, I've been and gone and done it now.
I am now the proud owner of a 20" 2.4 Ghz iMac and looking very beautiful it is too.
Wife has not yet tried to use other than Safari (but I think I will put Firefox on it anyway) and is well impressed.
I'm having a Macnerd friend round next week to help me get the Time Capsule set up as external storage for the whole network and get the 3 windows XP machines to share the network.
Guess I'll have to invest in MS Office for Mac if my mate doesn't have it already.
Cool machine!