Here are the posted rules. Seems rather clear.

Qualifying Flight:

Qualifying flight segments include any fare that awards WorldPerks miles, including CyberSaver Fares, on flights taken during Promotional Period. Member must earn WorldPerks Miles on the flight for it to be considered a Qualifying Activity.
A qualifying flight segment must be flown on or between May 1 and July 31, 2002.
Flights must be operated by Northwest Airlines or Northwest Airlink flight numbers 5600-5979 (operated by Express Airlines I d/b/a NW Airlink) and flight numbers 2700-3600 (operated by Mesaba d/b/a NW Airlink) or Northwest-designated flights operated by KLM Royal Dutch Airlines.
Partner Airlines operated flights are not included.

http://www.nwa.com/offers/flyfreefaster2/