A differential backup is an incremental. Please use that terminology or it becomes hard to talk about this. As Jason mentioned, the more changes that occur, the further (in time) from the full, the more time and larger this backup will be.

To restore the most amount of data, you always need:

- a full backup

- The last differential since that full backup

The schedule of your differential backups should be made to limit data loss, according to your business/environment/needs.

I'm not sure what you mean with "daily biases".

If you use the maintenance plans, you can have it create new files each day, with the timestamp in the name. If you only want to keep one day's worth of files, and if you are sure you are backing things up to tape every night, that might be OK. I don't recommend it, and I have EVERY backup with a unique file name.

There are lots of scripts here: http://www.sqlservercentral.com/search/?q=SQL+2000+backup&t=s