I would like my program to write values to a computer registry when it is installed so that the program can run for only a certain number of days. How can i do this? If there is any other way to do write a program so that it works as a trial version, I wouldn't mind using that one as well, provided it works well.

You can access the registry through the Registry class.

There is
Registry.LocalMachine (shared)
Registry.CurrentUser (current user)

Then you use the .OpenSubKey( keyname ) and eventually .GetValue() to get the data, which needs casting to the appropriate type.

Regards,

Dominic