[Samba] how do windows users change their passwords in a PDC

[cisco]

I have Samba set up as a PDC and I have the global parameter 'unix 
password sync' set to yes (which should change the password in both 
smbpasswd and /etc/passwd). I can't seem to find any documentation on 
how the windows user can change their password. I've tried ctl-alt-del 
which brings up the the windows security screen and clicked on change 
password but it does not take. It complains that my user name or old 
password is wrong or I might have my caps key on.