According to GameFaction, the release date of Grand Prix 4 has been put back a few days, to May 24th for PC, and 14th June 2002 for Xbox. This may be so that it does not release on the same day as F1 2002 (17th May).
Also, we've posted yet another screenshot for GP4, this time of the pit crew on an Arrows. Thanks once again to F1 World. You can view the new screenshot here.