I run Flex Builder 3 on a mac and as my project grows - the compile time gets longer and longer and longer. I am using some SWC\'s and there is a fair amount of code but it
Usually the first build takes the longest, and then it's pretty quick after that. That's using Vista x64 w/ core 2 duo.
Otherwise, I am nearly certain a Intel Core i7 Extreme Edition 965 3.2GHz upgrade processor would speed your Flex building up nicely .. :) :) :)