The largest source of information on Irish and Scottish music on the Internet is the wonderful Ceolas site, found here:

http://www.ceolas.org/ceolas.html

An excellent on-line resource for musicians interested in Irish traditional music chords/ABC is the O'Neill's site:

http://trillian.mit.edu/~jc/music/book/oneills/

For Scots and Scots Gaelic, try starting at the Scots-L music and culture resource page, with links to the best information sites on-line:

http://www.tardis.ed.ac.uk/~ibb/scd/Music/

To subscribe to the Scots-L music mailing list go here:

http://www.tullochgorm.com/

and to subscribe to the Irish tradition music mailing list go here:

http://listserv.heanet.ie/irtrad-l.html