If you run Flex on a multi core PC try a utility called SMP Seesaw (http://www.mlin.net/SMPSeesaw.shtml)
It doesn't allow Flex to process faster, but rather allows you to control how many cores Flex uses. Flex will grab 100% of both processors in a dual core PC when processing images, preventing you from doing almost anything else. Flex of course will process slower if isolated on one core, but it does allow you to multitask on the PC. The only drawback is that you can't do anything else in Flex as processing is not seen as a separate task and you can't run Flex twice. You need another machine with a networked drive to do that.