I have a Shuttle SS51 too, and I had the same problem: installed the latest SIS IDE drivers (which also upgrades your IDE controller to UDMA6 (ATA133) instead of UDMA5 (ATA100). This will solve all "lead-in" problems, but will give you another problem in return:
CPU usage when burning cd's and dvd's is always 100%!
Tried all options (turning off DMA, changing IDE channel, master/slave, different media, etc.), no succes....
Please let me know if you succeed in solving your original problem and especially solving the new problem!