FW CS3 is my staple, and I am having big problems since installing Snow Leopard.
Worst at the moment is that I cannot get the Fill/Stroke colours to display... they disappear as soon as the mouse has clicked...
The potential financial horror of being FORCED to upgrade to CS4 is too much to imagine... I own both CS3 Design Premium and Web standard.
Or, you could roll back your OS (or create a dual boot), since you know that is what caused the problem and that the earlier OS gave you a functioning system.
Software manufacturers cannot guarantee their software will work on operating systems that don't exist when they release their software. Fireworks CS4 predates Snow Leopard, too. Some Mac users report problems with CS4 on Mac OS versions earlier than Snow Leopard, so upgrading to CS4 won't necessarily solve your problems.