The info you seek is in sunsolve.sun.com.
You need to create a bge.conf file in /platform/sun4u/kernel/drv. I don't remember the syntax, though.
But, like I said in another post, it is better to let bge auto-neg. If you don't have the exact config at the switch, you won't be able to get a network connection. bge does a much netter job @ auto-neg than hme, qfe, or eri.