Using STSADM (all PS 2007 Service Accounts incase using the same account):
1. Change the account password
2. Open a command line prompt (Start -> Run -> cmd)
3. Change directory wherever STSADM has been installed, typically:
cd "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN"
4. Execute the following two command:
stsadm -o updatefarmcredentials -userlogin DOMAIN\user -password NEWPASSWORD
stsadm -o updateaccountpassword -userlogin DOMAIN\USER -password NEWPASSWORD –noadmin
IISRESET
5. Reboot the server.