dont waste your time w/ those, its a pain in the ass and the results aren't THAT good
go to the dentist and get
http://www.britesmile.com or
http://www.zoomnow.com/
if you can find a coupon online you can probably get it done for about $300
plus... it only takes 1 HOUR and you're done for years
trust me its a GREAT investment you'll be happy you did it!