My question is am I limited to this memory or should I try to get some DDR2 800 instead, and if I can, could someone suggest a specific type that would work with my CPU/mobo.
The MB makers can only test a small number of different RAM modules, so their list is not intended to list all modules that will work. You'd be better off going to the RAM manufacturers' web sites and using their memory configurators to find memory that is guaranteed by them to work.