I use the Soon command from the reskit but the AT command will work:

soon \\MachineName cmd /c "net user AccountName NewPassword"

I use a batch file:

echo on >password.log
@echo MachineName1 >>password.log
ping MachineName1 >>password.log
if %errorlevel%

0 soon \\MachineName1 cmd /c "net user AccountName1 NewPassword1" >>password.log
@echo MachineName2 >>password.log
ping MachineName2 >>password.log
if %errorlevel%

0 soon \\MachineName2 cmd /c "net user AccountName2 NewPassword2" >>password.log
@echo ** end of file ** >>password.log