Internet Explorer 6: Tools->Internet Options->Privacy tab. Make sure your level of security is Medium (default) or below. Medium-High and High will block cookies. Then click on the "Advanced button" and make sure First-Party cookies are set to "Accept".
Internet Explorer 7: Tools->Internet Options->Privacy tab. Click on the "Advanced button" and make sure First-Party cookies are set to "Accept".
Firefox 1.x.x: Tools->Options:Privacy Section->Cookies Tab. Check box "Allow sites to set cookies".
Firefox 2.x/3.x: Tools->Options:Privacy Tab. Check box next
to "Accept cookies from sites".
Macintosh computers:
Safari: Safari->Preferences->Security. Make sure the check
is not on "Disable Cookies",
either one of the other settings should be fine.
Firefox: Firefox->Preferences->Privacy Tab. Check box next to "Accept cookies from sites".