It is possible to download free Microsoft clip art on a Mac, as long as you have Office for Mac installed.
Internet Explorer and Netscape users: here's a how-to article for you.
Firefox and Safari users:
Tip: Start Firefox and go to Preferences > Main; select Always ask me where to save files, so you know where to find them.
Tip: Start Safari and go to Preferences > General; select a location under Save downloaded files to, so you know where to find them.