Close outlook via task manager

[scfisher]

I have a backup routine that copies a number of my files to an external source.
For this to run i need to have outlook closed so the "pst" files in various "user" folders to be closed.
I cannot work out how to close outlook at a particular time. Is there a command line that i can use/convert into a dos\vb script that would i could schedule

Thanks in advance Steve