Welcome MojoXN!
I’m surprised no one has offered links to useful free resources on the net, so here’s my contribution.
Tunes
http://www.thesession.org/
The Session: a searchable database and forum for exchanging traditional (more or less) Irish tunes. Free to join and use, and tunes are available in standard notation and ABC format as well as MIDI. Tunes come with “comments” which are usually very useful and offer variations.
http://tunedb.woodenflute.com/
Similar to The Session, but smaller and without the forums.
Tutors
http://www.whistletutor.com/
WhistleTutor.com, “focuses on teaching Irish traditional music on the tin whistle.” Offers beginner through advanced tutorials, and sports video clips in Flash, RealVideo, and Windows Media.
http://www.rogermillington.com/siamsa/brosteve/index.html
Brother Steve’s Tin-Whistle Pages aim “to help learners improve their understanding of Irish music and ways of playing it on this humble - but wonderful - little instrument”. Loads of information on a variety of topics from breathing through to advanced ornamentation. Music is shown in standard notation, not ABC, and sound samples are in mp3 format.
http://www.whistleworkshop.co.uk/
Similar to WhistleTutor.com and Brother Steve’s. The “Instruction” section includes lessons on the different kinds of Irish music, cross-fingering, ornamentation, and phrasing. Music is in regular notation, not ABC, and sound samples are usually in mp3.
http://kerrywhistles.com/
Kerrywhistles is the home of Phil Hardy, maker of Chieftain and Kerry whistles. There’s a Movies section on the site which offers a selection of Tutorial videos in Windows Media format. Phil also hosts some of his private stash of footage from gigs (e.g. Flook, Mike McGoldrick, Lunasa, etc) which are wonderful and provide great inspiration.
As others have said, it’s important to take some grains of salt with you as you venture through these resources: there is no set method to learning an instrument, and the whistle is no different. The way site #1 suggests doing a crann might differ from site #2. Feel free to experiment and find what works for (and sounds good to) you.
Enjoy yourself, and watch out for WhOA!
Brett.