Hey,
The XP website gives details of the differences, i always had Pro untill i got my new Laptop, i now have home, and can i notice the difference? Nope!. I know there are differences but the majority of us wont notice the difference. To be honest, i have had far less issues with Home than Pro, Pro seems to have more to go wrong with it, its prob just me and my poor usage of it though.
Pro normally costs £80 ontop on the PC, and if i ever want to access a domain at uni there are things that you can download free to do that. Not sure what they are as my college gave me mine, its that rubbish, errr, i cant think, its the one that makes SUSE.