we provide a tool for exporting mojoportal skins from Artisteer.

you can create designs in Artisteer and export them as mojoportal skins, it should work reasonably well for most designs created in Artisteer but we don't claim it is perfect, in some cases people end up tweaking things in the exported css and markup files.

I'm not aware of any capability to import designs into Artisteer from other places, nor can the exported mojoportal skins be re-imported back into Artisteer. Artisteer has its own .artx file format so if you find a place to download files in that format it would probably work.