Somewhere in your thread on this forum, you need a line that goes <b>soft version</b>: that is, the first part is the software name as supplied to the function, then a space, then the version as a string (if you include "v" etc. in the post, you must also pass your version with this to the function). The parameter "prop" is used for the name of the property saved to your user prefs file. Note that if your post (or really, any front-page follow up) includes the same bolded version string, only the first appearance should be checked against.
For example, let's say your post had:
My Software v1.1
When you run check_version(), you would call as such: check_version("My Software", "mysoft", "v1.0", 9876).
This assumes a post number of 9876 for your script's thread, and will result in a property "_version_mysfot" being set to "v1.1" (which is cleared each day by mafia itself, and how the script knows whether it should check each time it's run; if the property exists, it can quit since it's already checked once today). This example also assumes that your user is running an older version of the script than what your post has been updated to report.
Edit: Ninjas everywhere, geez!
Edit2: It's possible that you may want to use a much shorter, or differentiated-by-user or something property. There's really no compelling reason to have "soft" & "prop" be different in most cases, but it's there just in case. You're also correct about the lack of relation between the function parameters & the files as they exist attached to your post.