I too have had problems writing and reading data DVDs. After burning files
to a DVD explorer would not list the files even though Vista was showing how
much free space I had on the disk. At times the drive would simply stop
writing and another custom coaster was created.

In an effort to solve this problem I upgraded the firmware but it still did
not work consistantly. I then came across some information that indicated
the DVD must be connected to the motherboard using an 80 conductor cable.
Sure enough after changing out the existing 40 conductor cable to an 80 the
drive works fine.

This setup worked fine on XP but for some reason had problems with vista.
Hope this can help others who are having similar problems writing to and
reading from DVDs.

Drive is an ATAPI DVD DD 2X16X4X16 ATA device
Upgraded the firmware to G7Z9 (this may not be the latest but it works)