Hello,
Just found out how to sort this in a 2820n using a set of commands that aren't in the Telnet manual. (it was on an Australian Draytek forum??????)
To find out if anything is set in the router currently, use:
srv dhcp priWINS ? for the Primary WINS and
srv dhcp secWINS for the secondary WINS
to set a WINS server address for the dhcp server to push out, just replace the ? with the address you want to use.
It really is that simple.
Andy