is tír Mheiriceá Thuaidh í: incorrect. "Meiriceá Thuaidh" is not an adjective, but a definite noun, and tír Mheiriceá Thuaidh can only mean "THE country of North America". (Whether that makes sense, is of course a different story.) It is fully definite, and so it cannot be put into a classification sentence ("is A country"), it could be only put into an identification sentence (is í tír Mheiriceá Thuaidh í = "it is THE country of North America").
What you are looking for is is tír Mheiriceánach Thuaidh í Stáit Aontaithe Mheiriceá. It might look a little awkward to start with, but it is indeed the recommended usage. As regards the í, I think it should be replaced by iad noting that Stáit Aontaithe Mheiriceá is a plural form, but as countries usually are referred to by a feminine pronoun, I would tend to keep the í.
I'll take a look at the rest of the grammar as soon as I can, but I just felt I should jot down this grammatical note. Panu Petteri Höglund 00:20, 11 Meitheamh 2007 (UTC)