Mac OSX Lion. Had trouble getting ReBirth to recognize mounted ISO as properly "inserted CD". Trick is to make sure the mounted disk is labelled as RB338V20.
- Double click ISO file to mount it
- Crossover Configure menu/Manage Bottles/Control Panel
- Launch Wine Configuration
- On Drives tab you should see RB338V20 mapped to one of your drives
- Show Advanced...if Label field is blank this is your problem
To fix...
- Copy Path, e.g. "/Volumes/RB338V20"
- Remove whatever drive it was mapped to
- Add new drive, e.g. "D:"
- Paste path (e.g. "/Volumes/RB338V20") back into Path field
- Select Type "Autodect..."
- Enter "RB338V20" into Label field
- Leave Serial: field alone
- Apply
Relaunch ReBirth and it should find the CD image now. Hope it worked for you!