I responded in the other thread........
I run it on SP3 with no problems. Try uninstalling > reboot > disable any anti-spyware or anti-virus > Install LogonXP > re-enable anti-spyware/anti-virus > reboot > try installing new Logons.........make sure you are using XP Logons and not LogonVista versions.
oh and by the way....it will not work if you're on a domain