Can I use clip-art commercially?
You have some clip art in your PowerPoint (or other Office document) and want to know if it's ok to use it for a brochure, advertisement or other purpose.
Visit http://www.microsoft.com/permission and follow the link to "Clip Art and Sample Art". There you'll find more information and links to other pages that may answer your questions.
Microsoft's page explain the uses that are legitimate for clip-art supplied with Office or other Microsoft products. Generally speaking, you may use MS-supplied clip art relatively freely in your own projects but you may not sell or redistribute it
Please do NOT take what you've read here as legal advice. Read the permissions document on the site carefully and seek qualified legal advice to answer any questions you may have.
And be certain of the source of any clip art. The fact that it's in an Office document or on your computer doesn't mean that it came from Microsoft. Another company or individual might own the rights to it and have entirely different terms and permissions.