AS far as know only ITVN is contractually allowed to show the Ekstraklasa in the US, and they are only available on the DISH NETWORK via satellite. However, I can't confirm it, as when I tried to have DISH installed in my house (for the sole purpose of watching Polish soccer), it turned out that the trees and the mountains were blocking the signal. So, of course, there is another option: sopcast and justin tv. You can watch virtually any Ekstraklasa game, although the quality sucks.
Yep. I second that, watched Tomciotv channel on justin tv, and the quality was really good last weekend.