Upgrading from:

Graphics`Spline`

Some of the functionality in Graphics`Spline` has been added to the built-in Mathematica kernel.

Load Splines` to use Spline functionality:

Version 5.2 << Graphics`Spline`;
Graphics[Spline[{{0, 0}, {1, 0}, {1, 1}, {0, 1}}, Bezier]]