All the functionality in Geometry`Rotations` is now available in the built-in Mathematica kernel function RotationTransform.
In Version 6, you get a TransformationFunction that represents a rotation in 2D by θ radians about the origin:
RotationMatrix rotates points in the opposite direction from RotationMatrix2D:
Similarly RotationTransform rotates points in the opposite direction from Rotate2D:
RotationMatrix uses yaw-pitch-roll angles rather than the Euler angles used by RotationMatrix3D: