Try this, go to the Asus site, and the page for your mobo (I believe this is it: http://usa.asus.com/product.aspx?P_ID=kPGmtxee5RsQVsXG
) and then click the download tab.
Choose Windows 7 64bit
Then go down and click the + next to Utilities. Scroll down about 3/4 of the way and you should see the AMD AHCI Driver v3.2.1540.24 and it'll rattle off the elephant's share of the OSes the file supports. This driver set should have the folders you need in it for 64 bit Windows 7 installation.
If this is what you've tried already, then there's either a problem with your USB drive or USB port. I had a friend who had a similar issue not too long ago and he swapped out the flash drive and it worked. Go figure. Crossing my fingers for you though. Let us know?