I’ve been using my computer in Irish for a while now, both my work and home PC. If there is interest, I’d be more than willing to publish a tutorial on how to do this along with a list of vocabulary to assist learners in navigating the interface once it’s changed to Gaeilge.
There are a few restrictions. You cannot use the default MS tools to change the language if you have Windows 7 Home Premium. You have to use a free 3rd party tool but I cannot really say anything about the software’s quality…
The Language Pack for Windows 8 RT (Surface RT and other tablets) is not available.
If you own Office 2013 neither the Irish Language Interface Pack nor the Irish Language Pack (for proofing) has been completed yet.
If you want to proof documents in Irish you will need to purchase the Irish Language Pack (US$ 25.00, I believe) from MS. The Irish Language Interface Pack is free for Office 2007 and 2010, though.
Since I would be doing this I figure I could throw in how to change FaceBook to Irish with some vocabulary there as well.
Here is a screen shot of my Windows 8 PC with Irish as the interface language.