WSS has some limitations, which need to be taken into account when installing the RadEditor for MOSS. The default rich text editor does not support Reusable Content and selecting images/hyperlinks, because these feature require the MOSS asset picker dialog. Therefore you will have to use the RadEditor built-in tools ImageManager, HyperlinkManager, TemplateManager instead of the MOSS specific MOSSImageManager, MOSSHyperlinkManager, and MOSSTemplateManager. If you try to use the MOSS specific tools in a WSS v3 webpart or list, you will get a client-side exception , because the editor is not able to load the asset picker dialog. You can disable the MOSS specific tools by modifying RadEditor's tools file (ToolsFile.xml). See the Removing tools from the toolbar
article in the editor documentation for more details.
All the best,
the Telerik team