My third attempt finally worked, although technically, it may well count as the first since I was trying to install BeleniX the other two times. This time, I downloaded the OpenSolaris combo live and installation CD, and noted that it recognized my wired Ethernet. It did have issues with sound and WiFi though, although I figured that the wired Ethernet meant I could solve those eventually. The thing is, the Intel WiFi Link 5100 is supposed to be handled by the iwh driver, which is supposed to be loaded in the kernel but it doesn't seem to be detected. Saw somewhere that an incorrect entry in device_aliases (can't seem to find it on my drive at the moment) and correcting that could solve the wireless thingy.
As to sound, I tried the opensound driver from opensound.com but still no joy. Not a high priority at the moment but I still would like to get sound in OpenSolaris eventually. Otherwise I'd still have to boot to Vista.
Speaking of which, I don't know if it had anything to do with Vista, but I first booted to my Vista partition earlier, then rebooted to Solaris, and couldn't get google and fastmail.fm resolved. I then shut down, thinking there was something from Vista that survived the restart, but still no google or fastmail.fm. So, I manually dropped dhcp on gre0, then started it again. That did it. Sure hope I don't have to do that often