I've just created a very small VM for installing OpenSolaris onto my ESXi box. The ISO CD booted in live mode to the desktop and I selected the option to install to disk.
The installer loaded, but at the point of "Finding Disks", the installer seemed to hang and no disk was found, even though format was displaying the disk okay.
Upon further investigation, I realised that the amount of RAM I had assigned to the VM (512MB) was causing a problem. By increasing this to 1GB, the disk was found and the installer worked as expected.
My guess is that this is due to Solaris deciding that with only 512MB of RAM, that some swap would be necessary, but it's not able to create it. Only a guess, but at least I now have a workaround.