Where is the central cache located in Bridge, so that I can clean it out?
On a Mac it is in the User library / caches/Adobe/Bridge CS6. Per OSX 10.7 the user library is hidden by default. Use menu Go with option to reveal this Library.
Don't know the location for Windows but if you are not on a Mac please provide more details about your OS
I have a PC so and am using CS4 still. So I don't know if it's in a different place or not. The program keeps telling me there is not enough memory to perform this action as well.
Go into Edit > Preferences > Cache , you'll see the path under 'Location'. Clicking the Purge Cache button will clear the cache.