With the release of Q1.2009 we have introduced changes that affected the custom skins of our controls. We changed the CSS names of almost all of RadControls in order to put them to conform to a unified naming convention, and this is why your custom skin appears broken. This was announced in our blogs prior to the release:
You may use our online skin converter that will make the older skins to work with the new CSS naming convention.
the Telerik team