Wikipedia info about the tournament
. Follow link above for the ticket seller Eventim (respected pan-European event booking and ticket agency). Don't know about re-sellers in the US like Ticketmaster. In Europe you often can book complete travel packages via agencies (bus/flight, hotel, guaranteed tickets).
The tournament will be held September 7 - 20 in Poland, in several cities. Tickets in the preliminary round usually buy you entrance for a day, so two games in the same arena. E.g. say you want to watch September 8 in Warszawa
when Spain (Rudy, Ricky, hopefully Sergio, ...) plays the UK (likely Deng, Freeland, ...), and Slovenia plays Serbia in the preliminary round.
France (Nic, TP, Turiaf, ...) still needs to finally qualify in games against Finland (Petteri) and Italy in August (each one home and away). If they do as far as I can see they would play in group B with Russia, Germany and Latvia in Gdansk (tough one).
Tickets are grouped in three price categories (15, 20, 30 Euro). I assume it doesn't sell out that quickly for the preliminary and qualifying round, and there can still be tickets had closer to the tournament, for some games likely even on the day of the game. Spain was pretty well visited (of course especially when Spain played), but I remember previous tournaments in Turkey and Serbia with many empty seats. Semifinals still has tickets available. Finals looks booked out (see travel agency hint above if that is what you want and you believe our guys make it).
Just a heads up especially for the European BE readers if you already have plans for September to be in the region... ;-)