Don't allow user to change password. While it is easily done via lusrmgr.msc in advanced versions of Vista, Vista Home edition has a different approach, thanks to Windows Vista Forums.
cmd console must be started under administrator, not just any admin account. So, to start this, either use the Run As... or "Ctrl-Shift-Enter" after typing "cmd" in Start-Run prompt.
Then, type in: net user username /Passwordchg:no
and hit Enter.