A friend of mine told me she has problems running telerik controls under Internet Explorer 8. I recalled reading somewhere there is a tag you need to add to your page in order to force IE 8 behave like IE 7 (where telerik controls work great), I did some search and here is the tag:
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />
Add it to your pages head section and you should be ok with telerik controls.Edit: as
Veskoni commented out, telerik controls are fully compaitable with IE 8 since
Q1 2009 SP1, so it will be a lot better to upgrade to that version (or above).