If you hang out over at AVS, you could ask the question about Tyvek, I'm sure someone has tried it before. I guess my only concern would be light loss through the product. The reason many people use BlackOut cloth (drapery lining) is that no light passes through, that is what you want, otherwise the picture will suffer. The Blackout cloth is a great DIY method and can be found at most fabric stores like JoAnns.
Depending on how big of a screen your building, the best bang for the buck is the Durotherm Lite Panels from Parkland. For about $28bucks you can get a 4' x 8' piece at Menards. Just trim it to your desired size, hang and enjoy.
