I don't see much in the 'ndd' (or 'ce') man page that would point someone unfamiliar with the procedure to the correct parameters.
The solaris 2 FAQ is probably a better resource.
http://www.science.uva.nl/pub/solaris/solaris2.html#q4.13
4.13) How can I use full-duplex ethernet?
--
Darren
ndd /dev/ce \?
will show you all of the configurable settings for the interface. You then need to disable or enable which ones you need.
eg (it may be different for a ce driver)
ndd -set /dev/ce adv_100fdx_cap 1
ndd -set /dev/ce adv_autoneg_cap 0
But you need to put these in a startup script in rc* as these settings will be lost after a reboot.
you can also force these settings with some /etc/system parameters, thus bypassing additional start up scripts.
add the following to /etc/system for your particular interface
set hme:hme_adv_autoneg_cap=0
set hme:hme_adv_100T4_cap=0
set hme:hme_adv_100fdx_cap=1
set hme:hme_adv_100hdx_cap=0
set hme:hme_adv_10fdx_cap=0
set hme:hme_adv_10hdx_cap=0