loosing rooms and networks due to formation of PC is a main prob for users using hamchi nowadays.
I GOT A SOLUTION.
1.Just before formating PC click start, Run, and type %APPDATA%
2.Youll see a folder called Hamachi.This folder contains the main thing for the hamachi including rooms,networks,configuration,data etc.
3.Copy this folder to a CD or Disk(If u r formating the whole system) or copy paste if to any other place of the PC u r not formating.
4. After formating install hamachi.
5. Paste the Hamachi folder mentioned above in to %APPDATA% .
6.After u login into hamachi ull have the rooms and networks.
7. Enjoy