Here's how to tell:
1. Go to the Finder.
2. Click on the Apple in the upper-left corner of the screen.
3. In the menu which appears, the first item should say "About This Mac" or "About This Computer." Slide your mouse down to that item and release.
4. A window will appear, similar to one of the following. Hopefully it will be obvious to you which version of the Mac OS you're running. WeaveMaker doesn't care about the details of exactly which version of Mac OS X or Mac OS 9 you're running (that is, 9.2 or 9.1 doesn't make any difference). So while the details may vary on your computer, these images are a general guide to what you'll see.