If it plugs into the dock connector, you will have no problem. If it plugs into the headphone jack, you may not be able to use it.
Below is the iTrip that I have for my Mini.
Notice the "nob" beside the jack. The iPods no longer have that little connector beside the headphone jack, so if you have an iTrip with this connector (I don't know whether the iTrip for the 4Gen iPod is like the one for the Mini), you won't be able to use it with the new iPods.