to update Power CMS 1 to be compatible with IE 9, you will need to own HTML Editor 3 and Security Assist.
Otherwise Power CMS 2 has been updated for IE9 compatibility. Power CMS 1 will not be updated.
Power CMS 1 uses the FCKEditor package which was discontinued before IE9 was released.
Power CMS 2 (And HTML Editor 3) has been updated to use the Newer CKEditor which does support IE9.