Current version (.5b) is Postcard-ware; if you use it, please snailMail me a (humorous) postcard of your hometown. The official release version will be $15. I'll release that when the app can handle more than just 1" x 2 5/8" (ten-up, three-across) labels.
Current version supports OSX 10.3.3 although it is probable that it will run in 10.2.x. There will be an OS 9 version eventually.