The CD-ROM seems only to be included with the PC Pack. The CD-ROM has "bonus" material and most likely also includes the software needed to go along with the Tree Microphone. You can access Tamatown with just your V4.5. The microphone lets you command your Tamagotchi to get mail and do other features, because your current Tamagotchi will appear on your desktop.
I believe regular Tamagotchi V4.5 packages will include just the Tamagotchi.
The user Takatchi took a picture of the V4.5 PC Pack (American version I think). I could see that the PC Pack had a Tree Microphone, a globe design shell (think of an atlas), 4 little figurines and the CD. I think the mousepad was hiding somewhere I couldn't see it.