From the Ticketmaster website:
"Occasionally, some events will be available to purchase over the Internet in advance of the general public onsale. These presales frequently require a password that may be distributed by the venue, artist, team, or promoter of either the event or the presale, or distributed by Ticketmaster. Often, these passwords are distributed to exclusive members of clubs or certain other types of groups and cannot be offered to members of the public. Links may be published on the Event Information page at the time of presale."
So it might be worth checking the Foofighters website at 0900 on Wednesday to see if there's a code there, otherwise you'll have to wait until general sales start at 1000.
See also here:
http://blog.ticketmaster.com/presale-ticket-tips/
However the necessary code might also be offered in an email from Gigsandtours.com if you subscribe to their newsletter:
http://www.gigsandtours.com/mailinglist/subscribe
(I note that Gigsandtours.com, rather than Ticketmaster, is the link provided from the Foo Fighters website, so that's likely to be the best site to book through anyway).