The Inland Waterways Association of Ireland has plenty of information. (By the way, if you're looking for info, don't search for 'Eire', which is the name of the country only in the Irish language. Use 'Ireland' and you'll get results.)

Here's a video complete with diddly-eye music, of people enjoying their cruising holiday. If you're going to Leitrim, it might be nice to hire bikes for a day or a half-day and cycle around.