While playing around with some XMI (XML Metadata Interchange) importing/exporting functionality, I found this great blog: MOdeling LAnguages. His service to convert from one XMI format to another is just awesome. Have a look at this site: XMI2 – A tool for exchanging UML models among CASE tools.
Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.