As you may already know, Xbox Live support is going down for all original Xbox games this April. Someone should really remind Microsoft that they said April as DLC for original Xbox games have already been taken down.
Reader Cliff pointed us to this NeoGAF thread where a number of people are complaining that they can't download DLC for original Xbox games anymore. Joystiq looked into the matter as well and found the same issues.
This whole ordeal raises an issue I never considered before. Once the online service is taken down, you may never get to play a digital only title ever again. Well, unless you illegally download the title or content of course.
[Update: Microsoft contacted Joystiq and stated this DLC business is an error. Microsoft is working on fixing this issue and people will be able to download original content until April 15 once the issue is resolved.]
Original Xbox DLC - Already Dead and Gone? [NeoGAF, Thanks, Cliff!]