Old MSWMM format from previous version of Microsoft Windows Live Maker is still supported in latest version, so you may be able to re-save .mswmm projects to the newer .wlmp format. As far as we know, this is the only mswmm to wlmp conversion that would make sense.
Convert Microsoft Windows Movie Maker project to Microsoft Windows Live Movie Maker video project.
We found one software available in the database for this conversion.
Microsoft Windows software - convert mswmm to wlmp on Windows
A proprietary video editor for Microsoft Windows
Convert from mswmm file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.