A new CD can be shared by simply inserting it into the CD ROM drive. The new disc will automatically be mounted on the desktop and made sharable to AppleShare if it was previously a shared CD (on that server).
If the CD had never been shared previously, the CD will mount on the desktop, but you will have to share it via AppleShare Admin. After that, simply dragging the CD to the trash to unmount it, and then inserting it again, will cause it to automatically mount and become sharable with the same privileges as it had previously.