The following tools can convert RTF documents to ODF documents.
Microsoft Office ODF Extensions
This Microsoft Office add-on allows Microsoft Office to open ODF documents and save Microsoft Office documents in the OpenDocument format.
Download Microsoft Office ODF Extensions from http://odf-converter.sourceforge.net/
OpenOffice.org
OpenOffice.org is an office suite that can open and save documents in many formats. This tool can also open RTF documents and save them as ODF documents.
Download OpenOffice.org from http://www.openoffice.org.