A general answer is difficult to give but what you should always do is make sure your code is valid. Then you should be aware of all the bugs, google for "ie6 bugs" and you'll find heaps of good info about what the bugs do and how to fix them. Also, adding this to your page could help but it's not guaranteed:
HTML Code:
<!--[if lt IE 7]>
<script src="http://ie7-js.googlecode.com/svn/version/2.0(beta3)/IE7.js" type="text/javascript"></script>
<![endif]-->
If you can't post a link to the site, you should strip down the unrelated code until only the problematic code remains and post it here.
Good luck!
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