From Yahoo - they dont seem to have a specific number:
Initial position eligibility for each player was determined based on past participation and information supplied by the teams during the off-season.
Players are eligible at one or more positions during the 2007-08 Yahoo! Sports Fantasy Hockey season, depending upon their real-life participation.
All position eligibility requests are reviewed by Yahoo! Sports and confirmed with our hockey sources. Due to the nature of the review process, we're unable to comment on each individual player request.
Updates are made during the regular season based on changes to the lineups and official team rosters. Players do not lose position eligibility when moving from one real-life position to another. So, if a right wing begins to skate regular shifts as a center, he's eligible for the remainder of the season as a right wing and center.
New positions are added when it is confirmed that a player's primary position has changed and that the change is not expected to be a temporary one.
When a player has earned eligibility at a new position, the position is visible on the pull-down menu on your team roster.