Adaptec have some updated drivers for the U160 range of SCSI adaptors under WinXP. They are listed on the site as Release Candidate 1 drivers and apparently are awaiting Microsoft certification and are dated 27-3-02
The drivers have been designed to overcome speed negotiation problems under WinXP with such devices as scanners, CDs & CD-Rs. I know a lot of people seem to have reported Buffer Underrun"s and the like when using some Adaptec cards.