samba - Sep 2003 - add user script question about -M %u and %m$

Hi,

I'm running samba (on debian woody) as PDC for Win2K,98 and XP clients. 
What is the difference between:

add user script = /usr/sbin/useradd -d /dev/null -g machines -s 
/bin/false -M %u
[ seen on p.399 in O'Reilly Samba Book ]

and

add user script = /usr/sbin/useradd -d /dev/null -g machines -s 
/dev/null -s /bin/false %m$
[ seen on SuSE's Office server and various websites ]

in the global section. Which version do I have to use?

Thanks
Marcus