You could use a registry key and read in that key to see howmany days, hours or startups are done.

Or you can make a file if your program firsts starts up. Encrypt this file or write into it in something that isn't directy readably by a text editor.

Both methods work but are really easy to 'crack' if you don't protect the data inside well ennough.

take a look at the shareware starterkit, it should give you a few pointers http://msdn.microsoft.com/vbasic/downloads/starterkits/default.aspx

Cathal