ATI has been allegedly working on its OpenGL 3.3 driver since the release of OpenGL 3.3 in the spring of 2007 and since this time ATI Radeon, ATI FirePRO and ATI FireGL cards  support this, not very popular API.

OpenGL is loved by universities and Mr. John Carmack with his Doom and ID5 engines and games but it's still important enough for GPU manufacturers to care.

ATI has announced that it will support OpenGL 4.0 with Radeon HD 5800 and Radeon HD 5900 series. The cards feature full OpenGL 4.0 support, including tessellation and integration with OpenCL API, enabling GPU acceleration for future applications.

OpenGL 4.0 is also supported by Radeon 5400, 5500, 5600 and 5700, with the exception that the driver for them cannot support double precision, a feature that will likely be implemented at a later date. You can read more about it here.

You can download the new driver here.