If you're having issues with getting the default nge driver to like your card, you may have better luck with Masayuki Murayama's nfo driver
. Search the page for nfo and you'll find it.
As it's pretty much just a raw driver, it's probably not appropriate if you're new to Solaris. The documentation is sparse, but if you're a Solaris veteran, you'll be able to figure it out; it has binaries and source. And an 'adddrv.sh' script!
Of course, with either nge or nfo, you have to remember to plumb the interface. If you haven't done that, I don't recommend looking into replacing the driver.
I realize the OP probably either got it working by now, or has given up. But, someone else may need this information later.
As my NIC didn't like the nge driver (or vice versa), I had to replace the driver. Maybe U4 (09/07) fixes the nge driver, I'm still waiting on the media. (But it ain't broke anymore, so I'm probably not going to go back to nge...
Best of luck to anyone who needs this message!