I discovered that you can have more than one backup for your Mac with OS X Snow Leopard’s Time Machine. I just disconnected my main backup drive, connected my portable hard drive, and selected the portable drive as my Time Machine backup drive in Time Machine Preferences.
Once the backup was complete, I ejected the portable drive and hooked my regular backup drive again. I then selected the original drive with the Select Disk button in Time Machine Preferences and Time Machine went along its merry way as if the disk had never been disconnected.
Unlike my PC at work that had to be restarted three times on Friday, Apple makes things incredibly simple.
This guy’s blog was especially helpful: