Here's an update on the status of the PC version of the Dead Money add-on in Central and Eastern Europe (which includes Czech Republic, Estonia, Hungary, Latvia, Lithuania Poland, Russia, Ukraine and likely other countries as well).
The add-on is still not available for the 1C/Cenega PC version ("fallout new vegas enplczru") released in Russia, Czech Republic and Poland, even when using the English language version of the game. The only official word so far is the Czech Cenega website, which says that it will be out on March 29 on DVD. Polish Cenega support says that Dead Money will be available in Poland, but does not say when. The 1C/Cenega edition has also recently been updated to 184.108.40.2062, which adds Dead Money compatibility.
Meanwhile, owners of the main Bethesda edition of the game (either retail or Direct2Drive) that reside in aforementioned countries are now able to purchase Dead Money via Direct2Drive (Steam still blocks them from purchasing it there directly based on their IP).
Note that owners of the 1C/Cenega edition (including copies purchased from Steam in Czech Republic, Poland and Russia) will still not be able to install the add-on after purchase from Direct2Drive, as the 1C edition and Bethesda editions are treated as separate games. Even if you have the 1C edition installed, Steam will still tell you to register Fallout: New Vegas before installing Dead Money. However, it is possible to register both Bethesda and 1C editions with the same Steam account. Save games from both versions are compatible.