How to install storm windows in a windowless screened in porch?

Before you do anything, check local building code. You will most likely need to pull a permit to enclose the porch. There will be a bit of framing involved. You can't just slap some siding up - what is going to frame the windows and hold them in place? Even if you do not insulate on the inside it should be done on the outside after the framing is complete, before the windows are installed and siding goes up. I highly recommend at least a consult with a licensed contractor to make sure you are building to local code and construction is completed correctly. In addition, check with your homeowners insurance carrier, this will be considered additional square footage. Property tax may also be reevaluated.

I'd install sliding glass doors. Great open in the summer (already has the screen) and easy to close up inthe winter. Much easier to install than windows of any sort.

Have you heard about the clear vinyl or plastic covers that you can attach to your wall? I found some similar here. You can roll them up I believe when you're not using them.