I managed to find the web site for this (
www.jumpcross.com). It has loads of info on it and its been quite useful.
Apparently there are teams of 2 people and it looks like the courses start at around 2'9". I think, however, there must be smaller ones because not everyone can jump that big.
It certainly looks fascinating. I'm waiting to see if my yard manager decides to take the plunge. I've also heard that our local cross country venue may be doing one.
Thanks for all your help.