Incremental backup just backs up what has changed since the last full backup. So you have to do the full first. In my opinion the best way to do any of the PPC backups is to do it through the Active Sync window on the PC.
The major choice to make in that screen, other than where to store the backup file, is FULL or INCREMENTAL and that's it.
I have mine jammed full and it took about 50 minutes to do the Full and then about 30 to do the incremental a day later.
Get coffee!
