In the US you have 1 year to file your patent. So subtract one year from Creative's patent date to get the date they can claim they came up with the idea.

However, the patent is totally frivolous and should never have been granted in the first place. it cleary fails the most basic requirements of any patent. The idea was not novel nor was it non-obvious to someone skilled in the art.

You might be able to get their patent overturned if you can show Creative themselves were using similar navigation in any product that predates the patent by more than one year. Other products to look at are Compaq's player and Diamond's original Rio - I'm not certain how those worked though.

Bruno