Your FCP capture scratch files and exported QuickTimes don’t work on your PC because they’re in a codec that isn’t on your PC. In other words, it doesn’t matter what the original footage was … what matters is how the media was captured/encoded on the Mac (in the case of capture scratch) and what codec the FCP sequence is in (in the case that you export self-contained QTs using the sequence codec, which is the default).
It’s important to understand that what I’ve only added more detail to doesn’t contradict what Todd said … basically, that you need to export from FCP using a codec that your PC has (unlike some of the codecs FCP uses). The PNG or Animation codecs are good for that purpose. Another option is to install the codec you use on your Mac on your PC (i.e., if you use AJA or BMD Uncompressed codecs or a particular flavor of HDV).
Based on the questions, it seems that you could save yourself lots of time and frustration by reading up on the subject since video codecs and formats are not a subject that one can just stumble through without understanding. Perhaps Google for some type of video codec primer that explains the basics.