Oh you want to import from an XML feed... I was thinking you wanted to export as an xml feed.
Importing is more difficult. I'm assuming you want to import a product list from an xml feed. Our tools really won't help much with the actual import in this case. You would probably have to hand code the import into the database using php or some other importing tool. Depending on the size and complexity of the imported xml file this could be pretty easy or complex.
I'd probably then do a CRON task to run the import php daily or however often you feel necessary.