Window Kit?

What's with window kits? What's the content of one? Are they worth the money or should I just make one myself?

I would say they are a waste of money if you already have the tools. just grab some nice gasket material to cover up any imperfections (unless you have an industrial laser there will likely be some) http://www.pcmods.com/list.asp?DepID=11&CtgID=9