Know any good localization companies?

My company has a program they want translated into Spanish. All the English language strings, icons, button graphics, etc are in standard .NET resource files (*.resx).

I gave the person in charge of finding a localization company a set of all the .resx files, so they can send them to various companies and get quotes.

So far, two of these companies have called back with a "What is this stuff? There's a lot of other data in these files..." as if they've never seen a .resx file before or are opening the things as text files.

Does anyone know of any good localization houses that you or your company uses that has a clue on how to handle .NET resource files?

Thanks