There are some infos about the game on the website of the "Deutsches Institut für Public Affairs" (in German):
http://www.dipa-potsdam.org/wissen/kanzler_forever_planspiel/1) You will be able to choose between the five major parties (SPD, CDU/CSU, Greens, FDP, Left Party.PDS).
2) The candidates are Schröder (SPD), Merkel (CDU), Fischer (Green), Westerwelle (FDP), and Lafontaine (Left). Some alternative candidates are also available: Müntefering (SPD), Stoiber (CSU), Gerhardt (FDP).
3) Apparently, there will be a targeting function for the individual constituencies/districts like in the Prime Minister Forver games. No info if or how exactly they´re gonna combine the PR ("second vote") with the FPTP elements ("first vote")of the German system.
4) In addition to 2005 there will also be a 2002 scenario (Schröder vs. Stoiber) included.