"Purchased a 1.5Tb external hard drive, mostly for storage of photos and movies. Been reading about partitioning and get conflicting advice. I am thinking about only 2 partitions - one for system and applications, and the other for data. My MacBook has a 160 Gb hard drive. Should I do one partition for that and to use Time Machine for backup?"
Yes, partitioning (at least in my opinion) is a GOOD idea.
I'd suggest you consider MORE THAN just two partitions. Three or four might be even better.
I'd also suggest that at least one partition (possibly the first one you create on the drive) be used to create a bootable clone of your MacBook's internal drive, using either CarbonCopyCloner or SuperDuper. When you do your partitioning, make the boot partition large enough for "future expansion" when the time comes to get a new Mac. 500gig might be a good size.
I would also create at least one partition that would be a "personal data" volume -- that is, to hold files such as music, movies, other data, but NOT system files. The idea is that your data files are probably of smaller total size than the system files. A smaller number of files is much easier to back up. You should probably keep a copy of your personal data files in at least 3 locations (on the MacBook, and on 2 backup drives).
The third partition might be used for "scratch storage" -- stuff that you save but consider "non-critical" and not in need of backing up. Things that you wouldn't care about if they suddenly "disappeared" on you. An example might be a movie you saved but wouldn't think much about if you hadn't saved it in the first place. Files like this take up a lot of space on your "main data drive", so put them in the "scratch" partition where they're out of the way.
