Once again, I'm using this site to store infomation I would otherwise forget. In a Slashdot article about air filtration, someone posted a very inexpensive way to filter a whole room. Just attach some polyester air filter material (the poster suggested 1" thick Blue Tint) to a large box fan. Seems simple enough, especially in a room with a generous amount of ambient noise (read: a server room, or my room since it has two loud computers and a fan already).