I am not sure. I want to have Windows 3.1 so I can use specific Win3.1 apps but I no longer have the floppy drive so I can't install it. Is there a way to legally install Win 3.1 with IMG? I don't think MS supports Win3.1 at all.
There's no free Win 3.1. But, you can get a USB floppy drive pretty cheap on ebay.
Now all you have to do is find an MS-DOS machine to install it on - did you remember that Win 3.1 needs MS-DOS? Copy the Win 3.1 install files onto a CD or the local disk first, because I don't think you'll have much luck getting MS-DOS to read the USB floppy.
Don't forget that 32-bit Windows OS's support running Win 3.1 applications - more or less. The x64 versions don't (at least I think the Win16 support is still there in 32-bit versions - you might need to check). It would be worth seeing if your regular Windows installation will run the program.
I really can't imagine what Win 3x apps you'd want to run except out of curiosity (of course, there might be more reasons to want to run MS-DOS: http://blogs.msdn.com/virtual_pc_guy/archive/tags/Gaming+under+Virtual+PC/default.aspx).
Finally, if you do go through with an actual installation, I hope you're planning to do it in a Virtual Machine - getting that stuff to install in a VM will be painful enough - I'd guess that trying to get it installed on a modern system is likely to be futile.
I have not done it myself, but sources suggest that 3.11 runs like a champ with Dosbox. I do know from personal experience that it runs just about any DOS app with ease.