The problem I had was driving me crazy, the write buffer in Nero would jump about between 97% then to 16% then to 55% then to 90% then to 4%... etc, etc.

Hardware as below.

Fixed the problem by installing the Release Candidate for
the Adaptec 19160 SCSI Controller

Which can be found here...

Driver Download Page

So if you are having similar problems with your SCSI setup... give that driver a try.

Hope this is of help to anyone