Last week, Time Warner (TWX) announced a $25 billion write-down. Now NBC Universal’s parent company, GE (GE), may be looking at one of its own, courtesy of Vivendi, which owns a 20 percent stake in the broadcast network/movie studio/cable TV outfit.

Vivendi will be writing down the value of its equity, which it acquired in 2004. A spokeswoman quoted in a Dow Jones piece says the write-down  will be “lower than the EUR2.3 billion [$3.1 billion] gain the company booked in the third quarter from the creation of Activision Blizzard Inc,” which leaves an awful lot of wriggle room.

As recently as last November, Vivendi’s stake was supposedly worth somewhere in the $6 billion to $8 billion range, which implies a value of of $30 billion to $40 billion for the entire unit. But Vivendi and GE disagree about the value of the NBCU, and the two companies have a complicated relationship, with competing put/call options in the stake.

NBCU reported operating income of $3.1 billion on revenue of $15.4 billion in 2007. Through the first nine months of 2008, the unit had posted operating income of $2.3 billion on $12.5 billion; those numbers included a big boost from the 2008 Beijing Olympics.

For instance, in 2002, Time Warner had to take a $54 billion write-down connected to its disastrous AOL deal. Today, the company has announced a $25 billion write-down, which is in part connected to… its disastrous AOL deal.

To be fair, most of that charge has nothing to do with AOL, but with problems in its cable business; spin-out company Time Warner Cable (TWC) announced a $15 billion write-down of its own. But while Time Warner doesn’t elaborate on the charges in its release–it just says they are “related to goodwill and identifiable intangible assets at the Cable, Publishing and AOL segments”–I’m told that some of the write-down does indeed relate to the original AOL deal from eight years ago.

Other problems at Time Warner aren’t of its own making: The company says it will also take a hit of $50 million to $60 million from a “restructuring of a lease for space in the Time & Life Building, held by a lessee who recently declared bankruptcy.” That tenant, I’m told, was Lehman Brothers.

In any case, as astonishing as these numbers look in print, they don’t have much to do with Time Warner’s performance as a company, in the present tense. But Time Warner had worrisome news on that front, too: “The economic environment has proved somewhat more challenging than the Company previously expected, particularly for the advertising businesses at the AOL and Publishing segments.” Sigh.