I have a site that has been developed that has two image sprites:
http://www.thinkshift.com.au/services/social-learning-memory/
There is a "home, about, services..." sprite which appears correctly in all browsers.
The second sprite "addictions, smoking cessation..." is meant to appear in the "mustard" coloured band but doesn't appear in IE6 or IE7.
Works perfectly in Firefox and Safari.