Seán (it's ALT 160, btw) :) is from the Norman form of John, Jehan, and Eoin is directly from the Greek form, Ioannes (as is Ioan and possibly Ian).
Ian is the Scottish form.
Similarly, Ean is the Manx form of John, and Ioan, Iefan (Anglicized to Evan), and Ieuan (that's the one my great-great-grandfather used) are Welsh forms.
**Vita Brevis, Ars Longa**
This message was edited 3/11/2008, 6:38 AM