Look at http://www.timebridge.com/lp/outlook.html

This is an Outlook plugin that works with a free web service and
allows you:
* to schedule meetings with people much faster than email or outlook
forms
* share your availability with other as if you have Exchange server
* share your availability with people working for other companies

TimeBridge got Editors' Choice from PC Magazine, and for good reason!

It is free and easy to use.

http://www.timebridge.com/lp/outlook.html