(I hope this hasn't already been posted here. I tried the dKos search, but came up empty.)
Nader turned in over 3,000 signatures to meet a 1,500 requirement. Given Iowa's relatively liberal petition rules (e.g., need only be an eligible voter rather than actually registered, no requirements with respect to witnessing signatures), that seems more than ample. In fact, the Iowa Democratic Party, ACT, and Rep. Boswell (D-Iowa) all had examined the Nader petition and decided against challenging it.
Nonetheless, hours before the challenge deadline on Friday, a Drake University journalism professor filed a challenge. A decision is expected by Wednesday.
http://www.dmregister.com/apps/pbcs.dll/article?AID=/20040821/NEWS09/408210337/1056