>Geoffrey Heard wrote:
>
>I can't find any instructions for Time Machine. The first thing it 
>wants to do, apparently, is to take total control of the HD I want 
>to use for back-ups. Is this normal? Can't it use just part of the 
>HD?

As Kino advised, one approach is to partition the backup HD.

Another approach is to store one or more disk image files on the 
backup HD whose total capacity is the maximum amount of data you 
might need to store on the backup HD in addition to your Time Machine 
backups.  You then can either store your additional data within the 
disk images, or else delete a disk image to make room for data you 
are about to copy to the backup HD.


>I'm about to embark on a trip using my #2 machine which, at the end 
>of the journey, I want to leave behind me with some other gear so it 
>can be there ready for use next time I travel to that destination.
>
>Now -- what I thought I would do was back up my #1 machine to a 500 
>GB USB HD using Time Machine, use that to put all my stuff on the #2 
>machine, then during the trip, let Time Machine do incremental; 
>back-ups from time to time.
>
>When I return, I thought I would plug that USB HD into my #1 machine 
>and use Time Machine to bring my #1 machine up to date.

I believe you can do it with Time Machine, but it would be a lot 
easier with a conventional backup program such as Carbon Copy Cloner 
or Super Duper.  (Carbon Copy Cloner can even save superseded 
versions of files, but you must manually delete some of them when the 
backup drive fills up.)  These programs have the additional advantage 
of creating backups that are bootable so that you can use them 
immediately in case your Mac's internal HD fails, whereas Time 
Machine requires you to buy another HD before you can resume use of 
the Mac.

To accomplish what you want with Time Machine is complicated because 
it associates a given backup with exactly one Mac, based on the 
hardware address (MAC address) of the Mac's built-in ethernet 
interface.  Therefore, you cannot create a Time Machine backup with 
Mac #1, and then continue backing up to that same backup using Mac #2.

If you want to use Time Machine on your trip, I believe these steps will work:

1. Before the trip, use Migration Assistant to copy your data from 
Mac #1 to Mac #2 before the trip.  Then, use Time Machine to backup 
Mac #2.

2. During the trip, use Time Machine for incremental backups of Mac #2.

3. When you return, use Migration Assistant to copy your data from 
the Time Machine backup to Mac #1.
-- 

Bob Stern