This message is displayed because Google have a policy of discontinuing support for older browsers, which now includes Internet Explorer 8. Currently, you can ignore the message by clicking the button marked 'Not Now' to the bottom left of the message window. Some minor features may not function properly if you do this, however, and in the future Gmail may no longer work at all. Further details can be found at http://support.google.com/a/bin/answer.py?hl=en-uk&hlrm=en-uk&hlrm=en&answer=33864.

You can resolve the issue in the mid- to long-term by either upgrading Internet Explorer to a later version, or by using a different web browser e.g. Mozilla Firefox or Google Chrome.

This message is more common on University PCs, as they generally run Windows XP which cannot support later versions of Internet Explorer. Most University PCs have Firefox and/or Chrome installed, so these can be used instead. If they do not appear on the desktop or in the 'All Programs' section of the Start menu, they can be downloaded using Internet Explorer.