Currently, the only supported compare functions for ARB_shadow are LEQUAL and GEQUAL (unless this was changed when the ARB_ extensions were promoted into the core w/ 1.4?). I’ve had a few situations where GREATER and LESS would also be quite useful, so I’d like to suggest adding them as valid comparison operators (and why not add EQUAL while were at it).
Wow. Totally ignore my post above. 
I just found the GL_EXT extension that does just what I need. Sorry - I didn’t think to look for another extension outside of GL_ARB_shadow that would allow for new ARB_shadow compare functions.
Thanks.