You may need to tell MacDrive to view the Mac session on your CD/DVD (this is the case if your disc has multiple sessions). This can be done via the following:

1 - Insert the CD/DVD into the optical drive
2 - Open "My Computer" (XP) or "Computer" (Vista)
3 - Right-click on the optical drive
4 - Choose "MacDrive -> Show Mac Files"
5 - Follow the on-screen instructions, the Mac session will now be displayed

You can also globally set MacDrive to view the Mac files on a dual-format disc by going to Start > Control Panel, selecting MacDrive, selecting the "Settings" tab and checking "View Mac files" (under "Dual-format CDs/DVDs").