New NIC added after OS installation ?
Get to the OK prompt, however you find easiest/least destructive.
e.g.
# halt ot STOP-A for Sun(not sure of the keyboard short-cut for intel version)
OK> boot -r
to rescan your system for new hardware
New NIC should appear as the boot messages scroll by, or if you miss that type in a command tool window;
# dmesg
to take a look at those boot messages once inside the OS to make sure that the OS is seeing the hardware.
Choose an IP appropriate for you network (DHCP also works).
use ifconfig to configure the NIC
e.g.
# ifconfig NICname 192.168.32.1
# ifconfig NICname up
NICname should be what dmesg shows as you network card is called.
# ifconfig -a
should now report that your NIC has the assigned IP and that it is up.
Of course there are GUIs in Sol8 now aren't there, but I don't know what they are, sorry.