> I've got a 21142 ethernet card in my PWS433a:
...
> supported Ethernet media:
>     media 10base5
>     media 10base2
>     media 10baseT mediaopt full-duplex
>     media 10baseT

> How can I enable 100baseT mode?  I have a friend with an identical
> computer/configuration, and his computer comes up in 100baseT mode
> and seems to work fine.

Are you sure they are identical?

I think there are two separate small cards that mount on the back 
of the machine and hold the media chip and connectors.  Check your 
system to make sure it looks like the other one.

Another way that might help is to do something like
>>>set ewa0_mode foo

 and hope that the error message will list the valid possibilities.  
 If it doesn't say anything about Fast or Fast-FD or something similar 
 that looks like 100 megabits, then I'd guess your system has a media 
 card with the 10base2 and 10base5 connections but no 100 megabit 
 support.