Use this command to run the script file: FileName.bat DomainName\UserName NewPassword
Note: Put the exact domain/server name instead of '.' or just username

 @echo off
rem other app pools
echo *** Updating app pool passwords
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o updateaccountpassword -userlogin %1 -password %2 -noadmin
rem central admin
echo *** Updating Central Admin password
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o updatefarmcredentials -userlogin %1 -password %2
rem ssp - new
echo *** Updating ssp password for new installs
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o editssp -title "SharedServices1" -ssplogin %1 -ssppassword %2
rem ssp - upgrade
echo *** Updating ssp password for upgraded installs
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o editssp -title "Default Web Site" -ssplogin %1 -ssppassword %2
rem osearch
echo *** Updating osearch password
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o osearch -farmserviceaccount %1 -farmservicepassword %2
echo *** MANUAL UPDATE NEEDED. To update the password, visit the SSP Web application page, click Search Settings, and then click Default Content Access Account.
rem spsearch
echo *** Updating spsearch password
"%commonprogramfiles%\Microsoft Shared\Web server extensions\12\BIN\Stsadm.exe" -o spsearch -farmserviceaccount %1 -farmservicepassword %2
echo *** Updating spsearch content access account
"%commonprogramfiles%\Microsoft Shared\web server extensions\12\BIN\stsadm.exe" -o spsearch -farmcontentaccessaccount %1 -farmcontentaccesspassword %2
rem restarting IIS
echo *** Doing soft restart of IIS
iisreset /noforce
echo on

Find more details @ http://support.microsoft.com/kb/934838