OK - you can do it in Windowblinds 7, but not on a folder-by-folder basis. That is, you can use an Explorer background which will stay the same for all folders. On the other hand, you can vary the transparency of the Explorer window, which can give quite nice results if you don't go overboard (you can go all the way down to completely transparent, which may make for a good screenshot but doesn't really work when you actually want to do something). So far, this is the only way I've found to do this for Win 7. Windowblinds cost me £13 (about $19) so it won't break the bank, even if you do only want it for this effect.