Looking at OpenGL.xs in the source, it seems that glpcOpenWindow (which is called by glpOpenWindow) is available only if HAVE_GLpc is defined - and I don't think that symbol is defined on Windows. The error message you see arises simply because the glpcOpenWindow function cannot be found. (I get the same as you when I call glpOPenWindow on Windows Vista.)

Probably worth seeking clarification about this on the POGL mailing list. If glpcOpenWindow is being made unavailable by design, then one would think that glpOpenWindow should likewise be made unavailable.

Cheers,
Rob