I wouldn't count on much support for Macs in this forum. They're great computers but the reality is that over 90% of the world population with personal computers own PCs. As such, most public forums address using a PC vs. a Mac.
That being said, you might want to check out the forums at deal data base dot com. They do discuss using a Mac every once in a while and there are Mac versions of many of the more popular applications used with a hacked Tivo. However, making backups, restoring images, and copying drives are pretty much confined to using a PC.
If you don't mind having an extra box sitting in the back of your closet you can pick up a used PC with everything you need to support Tivo drive upgrades for as little as $25 plus shipping on ebay. This includes the case, power supply, motherboard, CPU, memory, video card, hard drive, floppy drive, and CDROM. An old PII, PIII, or AMD CPU, 4MB RAM, and a 1-5GB hard drive are more than adequate for the task.