I was having problems as well on how to get to the internet using this board (MCP78S [GeForce 8200] Ethernet) and opensolaris 2009.06 because the NIC was not recognized.
To get out of this "catch 22" you can use nge as the driver for the NIC.
For this you don't need a compiler. After you are connected to the internet you can download gcc compiler and the preferred nfo driver.
Lets inform the system to let nge handle the device
#pfexec update_drv -a -i "pci10de,760" nge
(or add nge "pci10de,760" to /etc/driver_aliases)
#pfexec ifconfig nge0 plumb
#ifconfig -a showed nge0
nge needs just a little tweaking to work
your ethernet address is probably reversed (it's what I have)
so do as root
#ifconfig nge0 ether
now just reverse the order of the words delimited by : (do not totally reverse character by character)
and restart dhcp
#ifconfig nge0 ether 0:19:21:db:3c:5
#ifconfig nge0 dhcp start
I decided to use static IP:
echo "10.0.0.138" > /etc/defaultrouter (IP of your router)
echo "10.0.0.0 255.255.255.0" > /etc/netmasks
edit /etc/resolv.conf (DNS from your provider)
Switch to using the DNS servers...
dawbckup:/etc# cp nsswitch.conf nsswitch.conf.original
dawbckup:/etc# cp nsswitch.dns nsswitch.conf
dawbckup:/etc# svcadm restart svc:/network/dns/client:default
Step 4: Switch to a static IP
# vi /etc/nwam/llp
change the 'nge0 dhcp' to 'nge0 static 10.0.0.3/24'
svcadm restart svc:/network/physical:nwam
add 10.0.0.3 dawbckup
Do a restart (init 6) and you should be able to connect to the internet after you reverse the ip adress again
ifconfig nge0 ether 0:19:21:db:3c:5
Now you can get your gcc compiler and download the nfo driver.