Running a program to determine if installation is neccesary

[snapon]

We want to run a program which will determine if the installation is neccessary. This program is part of the setup. But how do you run a program which has not yet been installed?

One other solution is to run the program "before installing files". This will update the registry, so my setup can read the reg value. But how do I query this variable before installing the files?

[Ted]

I think you will find that it is often self-defeating to make those sorts of determinations for the user. What if part of the installation is corrupt on their system and they want to reinstall?

If you really need to do this, you can easily read a value from the registry. They are all queried at startup. To execute a program before any files are installed, you will likely need to be distributing on CD-ROM. This makes it very easy to run the uncompressed file. You could also include the file alongside your setup.exe and it could then be run.