AG,
I don't specifically know how to unlock the devices, but I can offer some
ideas of how to troubleshoot the issue.
When you press the Eject button on the DVD drive, do you get a message that
says this device is in use by another program?
If you do, then identify what program or programs use the drive, such as a
burning program. It's possible that such a program has a bug that doesn't
release the drive after it's finished with it. I've heard of instances of
where Nero does this.
Check Task Manager (right click task bar and select Task Manager) to check
on what is running that could be using the drive. Shut it down if you spot
such a user.
Check Vista error reports for indications of other problems that could cause
such behavior. Click on Start > All Programs > Maintenance > Problem Reports
and Solutions. Peruse the report for problems and recommended solutions.
I've heard of cases where a virus, or some malware, can also enable this
type of behavior (locking one out with red circle with line through it).
Great fun for the author of the malware. Scan your system for this
possibility.
That's all I have for now. Post back on how you do.