Search for messages to or from multiple people by using the OR operator in the To and From field in the Advanced Find's first tab. You can substitute a comma for OR.

From: microsoft.com or cdolive.com
From: microsoft.com, cdolive.com

Notes:
Also works with Automatic Formatting, Views, and Search Folders (OL2003) dialogs.
You can use the OR operator or comma in many of the other fields in the search dialog when you need to search for multiple words.