I use XP Pro/SP2 at home. The PC hardware is a bit slow.
I have got a 500GB hard drive mainly to use as a backup for my main
data.
Is there anything (perhaps in XP or in NTFS or from good sense) which
suggests that I'm wiser not to make the whole 500 GB into one partition?
First off, what is your "main data?" Do you mean your C: partition,
which contains your OS?
If you intend to image the C: partition with Ghost or equivalent to
the new drive and make a mistake, you can hammer the entire
500GB. See recent thread "please help : partition gone"
There are other ways to damage a partition, most often done by
making a simple mistake when using a utility.
Ideally, you should have at least 2 backup hard drives duplicating,
the data, and in that case there is no need to partition them.
There are many good backup schemes, but none will rely on a single
repository of backed up data.
In your case I recommend 2 250GB partitions for the backup drive,
with your backed up data duplicated in each partition.
Duplication won't help if the drive fails, but will give you some
safety against data loss should a partition be corrupted.
--Vic