Although I studied harmonization, it was geared towards Bach and later. For earlier music, you need to look at the sources directly. There's two things, basically, to consider. One is harmony, that is, the chords or more complex harmonic structures. Two is the voice-leading. You need to be aware of parallels. Interestingly enough, the same skills are required for ornamentation.
To get a basic feel for harmonizing regional tunes, look to the thousands of examples of tunes that were harmonized in keyboard mss. and prints. Many of these combine traditional counterpoint with the folk-flavor that is typical of lute settings for Scottish and Irish tunes. Look also at the song settings. You can pretty much always find something similar to what you need in extant sources. dt To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
