We use SnagIt 8 as well and it’s a great tool if you plan on editing the captured screen, far superior to windows paint. If you just want a print screen of your current open window, just press ALT + PrintScn on your keyboard. If you want all current displays on your desktop, click anywhere on your desktop then press ALT + PrintScn to captures all open windows.
Check out SnagIt. It has a lot of screen capture options. I have not tried a continuous screen capture but they may have something in there. One feature we really like is the ability to invert screen colors after capture. This works very well when writing documentation. It avoids those black screens in the document, which consume large amounts of toner.
Take a look at my blog entry Tools for documentation – screen marking & screen captures.