Project management software compatible with MS Project

The project management software provided with Ubuntu 5.10 is a nice lightweight MS Project clone. It's easy to use it when you're a MS project usual user. The problem is the file format : it's impossible to exchange project plannings with MS Project users or to work on a project initially designed with MS Project. I suggest to provide another software (www.openworkbench.org that should be ported to Linux, for example) or to improve this one.