If the second PC is also set up to map to U:, this should work for it as well. I doubt you'll be able to get this to work with iPad, but I could be wrong, that's a question best asked in the FM Go forum.
Be careful when using \ in text expressions such as a calculation to determine the file path like you are here. \ is the "escape" character that tells FileMaker to treat the following character literally. "\"some text\"" for example will evaluate as "some text" as a way to get quotes inside a calculated text expression. In File Path expression, I avoid this issue by using / in place of \.
thanks for your reply, I really need this to work with ipads so I will post the question there as well.