Vista - logon and logoff need

We are going to a web based time sheet accounting package. Our users need to
enter their logon time as soon as they login. They then need to enter their
time when they are shutting down their PCs. Is there a way to do this? I
have made an entry in the registery
HKeyLU\software\microsoft\windows\currentversion\run to call a .bat file that
does ""c:\program files\internet explorer\iexplore.exe"
http:\\pliganet\webtime.htm". This does the trick for logon, is there a
better way? No the tricky part the end of the day when shutting down. We
need the same webpage to open so they can fill out their time card.

Any ideas?

Thanks in advance
Steve K