this (1.5) version includes OpenGL Shading Language
AFAIK, OpenGL 1.5 does not include support for OpenGL Shading Language (high level shared programming language) as a part of its spec, but it is available as set of extensions:
In addition to additions to the classical fixed-function GL pipeline in OpenGL 1.5, the OpenGL ARB also approved a related set of ARB extensions including the OpenGL Shading Language specification and the ARB_shader_objects, ARB_vertex_shader, and ARB_fragment_shader extensions through which high-level shading language programs can be loaded and used in place of the fixed function pipeline.
AFAIK, NVidia does not support these extensions yet, but has plans to add this. Only vendor that supports these extensions for a moment is 3DLabs. [HOPEFULLY my info is outdated!]
We are speaking about OpenGL 2.0-style shader programming exactly in favor of these extensions (ARB_shader_objects, ARB_vertex_shader, and ARB_fragment_shader), which is AVAILABLE NOW at least for some (3DLabs) graphic cards.
If so I'd also prefer these instead of Cg because I don't want to tie my app to one graphic card manufacturer.
Btw, Cg works for more cards than just nVidias. It can compile down to a variety of cross-vendor extensions.
These extensions - ARB_vertex_program and others - really supported by vendors other than NVidia, so Cg will work OK also for them.
Additionally, don't forget about passing parameters to your shader programs - this is what JOGL-CG bindings do [looks like] really nice.