Not wanting to be Mr. Obvious, as often I find myself wrong, but a quick check of the OpenSolaris HCL
http://www.sun.com/bigadmin/hcl/data...mfg.page1.html shows that your particular model of Intel motherboard is not reported to work. While this is not the end all be all with OpenSolaris, it might be worth downloading the the Device Driver installation check CD and boot it on your system. It basically checks to see if it can match your devices to a device driver. If it comes back 100 percent it should run either OpenSolaris or Solaris u4 or u5. If it comes back with errors then my guess is that it would not work well.
https://cds.sun.com/is-bin/INTERSHOP...-F@CDS-CDS_SMI is where I found it.