Just so you know... the tartan that Colin posted above is "MAC Donald"... the Scotish name. McDonald is different...
Actually, there is no difference between "Mac" & "Mc" when it comes to prefixes before surnames. They are the same thing, and one is not Scottish and the other Irish -- "Mc" is simply an abbreviation of "Mac", and sometimes you will even see "M'" -- usually the result of a lazy immigration officer. The book "Tartan for Me" has a nice article about this. You find MacDonalds (and many other Highland & Lowland Scots) in Ireland because of their employment as mercenaries (galloglasses) for the Irish, as well as the settlement of the Plantation of Ulster beginning in the 1600's.

There are many different MacDonald tartans, though, mostly for the different cadet branches (Clanranald, etc.)

We dealt with this issue quite a bit in Genealogy section of the library.

Cheers!

Todd