A first MS-Project round-trip integration is available in CVS HEAD as part of ]po[ V4.0.

Currently open issues include:
- No support for calendars. This may lead to (slightly) changes project end dates
- No support for "time phase data": The MS-Project scheduler creates resource assignment on a per-day basis that are not supported in ]po[. Again, this may lead to slightly changed project dates.
- Problem with duplicate task names: ]po[ does not allow for duplicate tasks with a common parent. These tasks will be joined into a single task.

We'd be happy if you could try out the functionality. Please don't forget to attach an XML project plan when reporting issues. Please make use of the SF Bug tracker at https://sourceforge.net/tracker/?atid=579555&group_id=86419