OK, I was thinking of an INI file.
INF files are by default associated with setups, but they are sometimes used for other things as well.
When you look at the program associations for INF files
(in File Explorer, Tools -> Folder Options -> File Types tab), you should find the INF extension. Click on it, press Advanced which opens another dialog. There's an Actions list, in which you should see "Install". Select that, then click Edit, which opens another dialog. Under "Application used to perform action" you should see what program is used to run the install. On my system (XP Pro) it is:
C:\WINDOWS\System32\rundll32.exe setupapi,InstallHinfSection DefaultInstall 132 %1
I'm pretty sure you would replace the %1 with the full path to the INF file.
However, I make no guarantees this will work. I'm just pointing out what I found looking at the file associations. It may be different for different operating systems. But maybe it will give you enough to know where to start looking.
What you need to find out is what executable needs to be run to process the INF file.