"To use your Apple Magic Trackpad and all its features, update your Mac to Mac OS X version 10.6.4 or later, and then install the latest trackpad software. "
Snow Leopard (10.6) can't be downloaded, it's only available on DVD.
Here are the requirements:
- Mac computer with an Intel processor
- 1GB of memory
- 5GB of available disk space
- DVD drive for installation