[dnanian]

We're really not designed to synchronize folders on two computers like this, Jo*. So that part of this won't be possible.

As of Leopard, Apple strongly discourages sharing a startup drive between PPC and Intel Macs: they go so far as to suppress Apple Partition Map-partitioned drives (for Power PC) when you're running on Intel. So I'd suggest two separate drives, each properly partitioned for the Mac you're dealing with.

It doesn't make much sense to use a Sandbox the way you're describing, either: they're typically for more advanced users, so you might not need one at all.

Finally, you can certainly schedule as many backups as you'd like.