After you install Indiana May Release (OpenSolaris 2008.05) in your box, you may need install the following packages to setup your box as a Gnu/Gnome developer desktop:
$ pkg install ss-dev SUNWxwinc SUNWxorg-headers SUNWgnome-common-devel \
SUNWperl-xml-parser SUNWiconv-unicode SUNWiconv-extra SUNWgit
It's a little strange, that the gtk/gnome header files are shipped in the liveCD and got installed by default, but not the X11 headers (in SUNWxwinc).
Besides that, you may still need the CBE. If you already have the installation on other machine, directly copy them to your box could just work. Or, pkgadd(1) is still available to install the SVR4 packages.