How to stop sync starting from scratch after an error

I keep getting errors (-124) when trying to sync music to my iPod Colour (20Gb). The error usually occurs after syncing several hundred tracks (but does not always occur at the same place - e.g. it might get as far as syncing > 1,000 tracks). After the getting the error I want to restart the sync process, and have it pick up where it left off - i.e. I don't want it to re-sync all of the tracks that were successfully copied to the iPod during a previous attempt. Instead, the sync process starts from the beginning every time, re-copying tracks that are already on the iPod. Hence I will probably never complete a full sync of my music to the iPod.

How can I tell iTunes to copy only tracks which are not already on the iPod? (without manually cross-checking a list of 4,000+ tracks and selecting them individually)?