Q: Can I still play my original Xbox games offline?
A: Yes! This disables support for online multiplayer, leaderboards, marketplace and other online features but does not impact offline play.
Q: Does this impact Halo 2 PC?
A: No! Halo 2 PC will continue unchanged as it's a Games for Windows -- LIVE game and not for the original Xbox.
Q: When will this take effect?
A: On April 15, 2010 (that's today as I type this). We aren't saying exactly when we'll be flipping the switch.
If the loss of Halo 2 hurts too much for you to bear even turning it on today, give our a read to remember the good times.
Source: [Xbox Live Operations Blog]