are you running dell quickset program still ?
i dont know if it has any bearing on the media buttons, but i know that the Fn+F10 (eject cd drive) doesnt work unless you are running it
there might be a similar program required for the media keys / or that allows you to re-bind these keys to regular keyboard expressions
also, what version of winamp are you using?
b/c in winamp 5 there is global shortcut keys, which could be what you need to re-bind to the dell media keys
though i dont have a i6000, so this is just general speculation
ill try it on my roommates i8600 tomorrow