I don't know how to make my "wireless ad-hoc" or "routerless PC-to-PC" networks (the ones that you can't change their name) private.

Open the Network and Sharing Center and find the ad-hoc network's name. Click where it says "Public Network". In the "Set Network Location" window, click "Home network".Steve Winograd MS-MVP (Windows Desktop Experience)

The problem is that unlike my personal home network the"Public Network" is unclickable.

It didn't give you the option when you first connected it?

No it didn't.I think I' better admit that this is not quita big problem cuz I simply change my public network settings whenever I need features like discovery and besides my home network doesn't have any problems.consider this as a report.