You all forgot about beer!
On a more serious note:
There are several Americans that use this forum that has visited Wacken a few times, try asking one of them.
For example:
warthog
lxe / lex
LooseCannon
My best advice is:
Order your WOA ticket via Metaltix
http://www.metaltix.com/
make sure you get the three day ticket:
Ticket WOA 2007 - 3-Tages - W:O:A - All-In-Ticket - 02.08. - 04.08.07
http://www.metaltix.com/item_detail.php?item_nr=22840
Book plane tickets so that you arrive in Hamburg at the latest on August 1.
Book plane tickets so that you will leave Hamburg at the earliest on August 6.
Purchase tent, sleeping bag and isolated mattress to bring with you.
Make sure to get € (euro / money)
Don't count on being able to use your credit card at WOA
Read this thread:
http://forum.wacken.com/showthread.php?t=122556