one more question -
can time machine back up other external hard drives? i do a lot of video work and have another external hard drive that i would like backed up via Time Machine along with my startup disc.
Yes. However, by default it will exclude them. You have to go into preferences and remove your external(s) from the excluded list if you want them backed up.
Also, let me just head off a potential future post here if I can... first off, understand that Time Machine WILL fill your entire external drive if you leave it running long enough. That's not a mistake, that's how it's supposed to work. It will do incremental backups until the drive fills, then the oldest backups will start to "drop off" the other end (delete).
The only real way to control how big Time Machine gets is to give it it's own full drive, or to partition the only external you have. That way, when it fills up it'll just start dropping off the oldest backups.
Keep in mind the best back up to have is as old as you can get, therefore you want the biggest external drive you can afford/find.
Lastly, if you have a lot of large files that change very often, you might want to consider creating some folders and excluding them from the backup.
For example I have a folder where my eMusic downloads go. Now, I drag all that music into iTunes anyway, so I exclude the eMusic downloads folder from Time Machine. If I didn't do that I'd end up with those same files backing up
twice... once in the "eMusic Downloads" folder, and again in the iTunes Library folder.
