I tested book it free on joomla 1.5.26 with a clean installation (no examples installed), but I can't reserve.
I installed mtupgrade, I have set it 1.12 n back end and fornt end, but the back end didn't work fine.
I have set mtupgrade on 1.2 on back end and it work fine (your guide say to set on 1.12 on joomla 1.5?!?!?), but I continue can't reserve on front end.
I installed SC Jquery but it don't resolve the problem.
The web site is marcoesposito.altervista.org/joomla-15-pulita/
You can register and after click on "lista oggetti" (list objects) on the left.

I'm waiting to test it for buy it.
I'm waiting for your reply.
Thank you.