I had all sorts of problems burning when moving from 2000 Pro to XP Pro. No changes to hardware whatsoever, just the software.

The built in XP drivers for an Adaptec 29160 are rubbish. They do not bus master or enable SCSI disconnect which gives a maximum transfer rate of 3MB/sec with very high CPU utilisation.

Solution. Install the lastest 2000 drivers from Adaptec's site. Burst transfer rates back up to 12MB/sec and CPU utilisation down to 2%. I can now write successfully at 12X once again