You may have hit the 915resolution bug thingamy Intel graphics cards have preset modes, and unless you're using one of the preset modes it says that the mode is not available.
there is a tool on the web called 915resolution, made for Linux (but can easily be changed to work for Solaris/OpenSolaris), that allows you to change the preset modes, and with a little tweaking you can place a script to be called before X display is started. I've got a copy of the modified code should anyone want it, it might fix your problem. This message posted from opensolaris.org
