I use a product called Cobian Backup. It's a pretty nice backup application that is completely free. It will backup files that are in use, such as Outlook .PST files. Really save for the lack of external media connectivity, it's a pretty full-featured backup program.

http://www.cobian.se/index.htm
http://download.cnet.com/Cobian-Back...-10071828.html

Note: I have no affiliation with the company that makes Cobian Backup whatsoever. I've simply used it in the past and found it to be a very useful program.

-SW