Yes and no. If an application is not multi-threaded then it will only execute on a single processor (on any platform, not just the MAC). However, when you have more than one processor, system programs (and any other programs) that normally have to fight for CPU time on a single processor system will have a better chance of getting CPU time more quickly. So in your case, your game may run a little bit faster but only because some of the other system programs will be running on the other CPU.
So, it will not act as if you have one 1.6 Ghz CPU by having two 800 Mhz CPUs, unless of course your application is multi-threaded and each thread performs equal amounts of work. I could be wrong but I doubt that is the case with most games. Now when you run many applications/programs at the same time you should see a significant increase in speed (or more accurately "significant increase in the rate at which work is done") by having two 800 Mhz CPUs vs only having one 800 Mhz CPU.
[ September 17, 2002: Message edited by: void main ]