although you will need to acknowledge their ownership of the trademark.
A suitable form of wording would be:
Outlook Express is a registered trademark of Microsoft Corp.
As far as disclaimers are concerned, it's not a bad idea to include one along the lines of:
Your use of the guide contained on this website is entirely at your own risk, and we wish to point out that we are in not connected to or sponsored by Microsoft Corp. For further information about Microsoft software please visit (then include a link to Microsoft.com)
Both items should appear at the bottom of each page of the site in Arial 8 point bold.