I'd echo the use of chain to weight the backdrop (the Main Stage curtain I controlled in college had 50lb of chain across the bottom to keep it hanging straight) also consider making it a few inches longer than you think you want it so that it won't move when you walk by or expose any of the support structure. Hope this helps.

Here are some interesting Links:

http://www.iweiss.com/curtains/rain/
http://www.distinctivefabric.com/fabric.php?id=VELOUR1
http://shop.store.yahoo.com/magiccrafters/clichertoor.html
http://www.backdrops.com.au/themes/show_cat.php?catid=46
http://www.godfreygroup.com/banner.html
http://www.laflinmagic.com/cgi-bin/web_s......match=on

If you check on ebay, you can pick up the framework for tradeshow displays cheap. With all the dot com companies going under, there are fewer of the these guys doing trade shows.

I picked up a 10' x 8' framework in a rolling case for $100. Add fabric and you have a nice free standing backdrop.

Be careful with some of those trade show frames. They can be very tempremental (and have non-standard components that can be difficult to replace) and some of the very light weight aluminum ones rely on the carpet fronts for a significant part of their stability. I've done a number of trade shows and I agree if you can find one intact that is a great idea however if you are going to retrofit something else to them, it could be more trouble then starting out from scratch.

The ones we used had magnetic strips down the sides of the carpet panels and they held together very well and allowed you to store a large surface area in a small space without having to worry about seams, movement, etc.