preparing for Time Machine

[Kevin Callahan]

Not knowing the details of Time Machine's preferences and options,  
I'd like to buy a drive BEFORE Leopard ships, so that the day I've  
installed Leopard, I'm all set for Time Machine.

Given I currently have separate external drives for photos, music and  
videos (I have 5 drives hanging off my MBPro) - -and considering I do  
a fair amount of audio and video editing throughout the day, is there  
some size ratio between my working data set (size) vs what I should  
plan for a backup drive?  I suppose it all depends on how far back  
you want to keep file changes in TM - so it's probably a dumb  
question, but ...

I've read you can define multiple drives as backup drives for Time  
Machine, so maybe I shouldn't worry about it.  But on day one, I'd  
like to have something in place.

Thoughts?

Kevin