Hi blueharmony and welcome to Piwigo forums,
As far as I know, users switching from Menalto to Piwigo did not use any automatic conversion tool. Most of the time, they restarted their gallery from scratch. If your lucky enough and have your title/description/tags written in the photo with IPTC metadata, then you can just use the synchronization feature and get everything back in Piwigo.
Having a conversion tool from Menalto Gallery to Piwigo would be useful since we see more and more users coming from Menalto Gallery. If you plan to create such a tool, let us know and we will help as much as possible.
Wow! I just came across this after I had started a thread myself: [Forum, topic 16866] How to convert metadata to titles
I did not succeed with the information provided there so far, so can you please post the procedure for using synchronization to populate title, description, tags and maybe even categories?