You should be able to do this with ACL.
There is a handy ACL command to save SGML as XML. Something like this would work...
xmlName = {your XML name}
if (doc_kind() == "sgml"){
save_as -xml xmlName
}
You would just need to write the bit that reads file from a target directory. Have Editor open each file, run save_as, and close it.
This assumes your SGML is in good order and will save cleanly to XML. If it was authored in Editor, you shouldn't have any problems.
Hope that helps!