The jQuery Timezone plugin allows you to show times on your webpage in the user's local timezone, even taking into account daylight savings time.
You need to include a version of the datejs library before the jquery timezone script. Either use the included or grab one from the datejs SVN:
<script src="jquery.js"></script> <script src="date-en-US.js"></script> <script src="jquery.timezone.js"></script>
See demo.html for usage information.