I am using InstallShield Developer 8.0 for my installation. I have the following scenarios for my installation:
1) If this is the first time installation is taking place on the system, do normal insatllation.
2) If user is modfying the installation, check for the version of already installed product and if;
a) Version of installed product is less than 2.0, then uninstall the old version (as the old version is entirely different than the new version and has to be uninstalled first for compatibility issues), reboot and continue with the new installation.

3) If user is uninstalling, just remove the product.
1 and 3 are very simple and are working fine. For 2, I have a custom action which checks the version of the product. I am not very good at InstallShield, I need input from you guys as to how to accomplish the item 2, especially (a).
I don't need to have exact solution, pointer to the related resource would be highly appreciated.
Thanks for the help.
Tomma