The wind resistance any bike rider encounters is based solely on the frontal area the rider presents. The larger the frontal area for the wind to hit, the more resistance will be encountered. If the heavier rider could somehow position him/herself so as to present the exact same frontal area as the lighter rider the resistance would be equal. Its not likely that could be done however.
This is a different force than the force needed to propel a rider forward on the bike. The heavier the rider, the more force is needed to move the bike forward (except on a downhill when the heavier rider has the advantage) so a lighter rider will not expend as much energy to move an equal distance as the heavier one, but both will meet resistance from a head wind proportionally to their frontal area.
