There are two ways to do this if you have DVD Tools installed: the "right" way and the quick-and-dirty way.
From a command prompt, run: "readcd dev=0,1,0 -f=test.iso -retries=32"
Replace the 'dev' value with the SCSI bus address used by your drive, and change the filename ('-f') to whatever you want. If needed, run "readcd -scanbus" to get the SCSI address.
OR...
Run the "Copy Disk" app from DVD Tools to copy the disk. When it finishes reading, it will prompt you to replace the disk with a blank one. Instead, open your %TEMP% directory (usually 'x:\var\temp') where you will find a very large file whose name is all hex digits (i.e. 0-9 + A-F). Move this somewhere else and rename it, then cancel the copy.
FYI... if you do this the "right" way, Copy Disk is still helpful: it displays the SCSI bus address as part of the "Source Drive" identifier.