I REALLY hate to sound like an idiot, but can someone please tell me how to use the installer versions of FML. Whenever I download it, I get it in a .jar format, and you can only run .exe formats. Can someone please tell me how to install it? I even tried changing the file extension to a .exe but to no avail. If it makes any difference I am running a Windows 7 OS.

Well it turned out I had to manually assign the java program to open, by default it only allowed me to choose from notepad or 7-zip, but now the cmd only shows up for a second before going way, and nothing happened. After printing screen, because it only showed up for a split second, it said: Error: Could not find or load main class. Is there anyone here that has had a similar, and can tell me a way to fix this? If not, I'll resort to Google, just thought I might get a better answer here.   

You've serverly screwed up your java install.

To manually run it just open cmd prompt, make sure you're in the same folder as the jar

And run:

java -jar {jarnamehere}

Otherwise, Google is your best bet to fix your file associations:

http://lmgtfy.com/?q=windows+fix+executable+jars+association

I just tried the cmd prompt and it says on mine "unable to access jarfile minecraftforge-installer etc". It's also showing in my downloads folder as a WinRAR Archive (it does this by default on any minecraft files (and some other files too) I download after something I did a while ago without knowing how and I've no idea how to fix it).

 

(Brainwave time - I just right clicked on the download file in the folder, opened with java, et voila!)

 

I suppose this could be useful if anyone else has the same situation as myself, even though unlikely, as double clicking on WinRAR Archive files just opens up another folder.