You can find the single-tune files in the ../X/ directory. You can search for a tune by name by going to the ABC tune finder page and typing in a title or fragment of a title. This will give you a list of all known ABC tunes by that title on the Web, with tunes in this O'Neill's collection flagged with .
The original O'Neill's Music of Ireland has been out of copyright for many years now. This collection of ABC transcriptions is copyrighted 1997-2000 by the contributors to the project. You are welcome to download anything here and use it, as long as you give credit to the transcribers, and take credit for any corrections or enhancements that you might make.
We are now in the "proofreading" phase, and everyone with a copy of O'Neill's is invited to examine any of the tunes that you download. If you find any discrepancies between the ABC here and the original O'Neill's, please send in the error reports.
Experimental gimmick: Tune List program lists all the tunes and provides conversion from ABC to various formats.