Hi Brooke,
I don't think you'll get much joy with TEDS on a Mac (unless you want to go down the virtualization route). Whether the work of Nathan Oates will help you depends on how you connect the Mac and the Topfield. IceGuide4Topfield is fine if you use a straight USB connection.
I didn't have that option because I have an NSLU2 (slug) connected to the USB port of the Topfield, connected to my wireless network, and no computer is anywhere near them. (An IceBox would probably have filled the same ecological niche but I already had the slug.)
I've made a custom command-line tool which downloads the Ice guide from icetv, generates the TGD files that the EPG_uploader TAP wants, and sends them to the Topfield by making an FTP connection to the slug. It recognizes titles of shows that I want to set timers for, and gets EPG_uploader to set those timers on the Topfield. It's still early in development and I have no interest in making a pretty front-end for it (sorry), but I am happy to share it with anyone who might have a similar setup. (Geek pride note: XSLT is a perfect language for operating on the Ice guide.)