Hi,
On the first run (or install) of the program you save some information (the date) to the pc. Every time the program runs, check the information versus the current date. Disable this check programmatically when the full version is installed.
That sounds easy, right?
The problem is preventing a smart user (also know as a hacker) of deleting this piece of information so the program think that it runs for the first time. I have only heard of 2 ways of doing that:
1) use the registry. Place several keys in different places (all microsoft folders as good because they are usually not cleaned by registry cleaners). Further more encrypt the information so that it does not look like a date.
2) Embed the information in another file. E.g. in the bitmap format there is unused space and it is actually possible to place the information here - and the bitmap will still look the same as ever.
Good Luck
Sunaj
'The gap between theory and practice is not as wide in theory as it is in practice'