PXE Plugin requires OpenSolaris 2009.06 build 110 or later. Also note that you need an "Automated Installer" image, not the LiveCD image. Download is availble from the following locations:
- OpenSolaris 2009.06 builds ISO (BitTorrent) — choose
osol-0906-NNN-ai-x86.iso.torrent
SPARC network installation is not supported