Yeah you're in a bit of a tough situation, for the reasons Brian laid out. It gets supper messy when you start mixing and matching from '09 and '10, as not everyone made the switch at the same time, and some companies went to 7" inbetween 6 and 8. If you do end up having to shell out for bindings, the new tech is really worth the money, but I understand that it might not be in the budget. Best of luck!
Edit: Here's a little chart that shows compatability of all the major stuff for the last few years.
http://www.evo.com/wakeboard-and-wak...formation.aspx