Moonfall Mask
Argh...I'll likely be researching until the cows come home to memorize the Latin and/or Greek to that extent...
sweatdrop
I'll make up my own language, how's that???
In all honesty, Latin is a hundred times easier to learn than English. There are just certain aspects of it that are not present in our language that really trip people up. =] If your school has a Latin program, or a local community college has one over the summer, it would be a good investment to take part in. Not only will it help with your story if you do decide to go the Latin route, but it is also a beautiful, interesting language to study.
You could also ask any Latin teachers that live near you for advice and perhaps to coach you on the side in Latin basics. Just some food for thought.
As for making up your own language, I would think that's more complex than picking up a dead language. O_O I mean, you have to take into account dialects, syntax, how other languages might have affected this one, parts of speech, conjugations, declensions, pronunciations, and a whole conglomerate of other details. If you want to pull a Tolkien and spend year upon year carefully crafting a language, then I say go for it. But if all you aim for is a Paolini move with a language whose vocabulary consists of whatever comes out when you bang your head against the keyboard, then don't make up your own. You could always shoot for a healthy medium, but I'm afraid that category is hair-thin and quite difficult to reach.
I dunno. Perhaps I'm letting my language geekiness get in the way with the whole "make up your own language" stuff. Personally, I would go with basing in Latin or Greek. That is so much more fascinating, since you can really delve in Roman or Greek history and show how your magic language became rooted in that society.
In the end, it's all up to you and how much effort you want to put forth.