Do you mean you are copying them from one computer to another? Or from one user to another? Or from one hard drive to another? The thing is, playcounts don't get saved in the song file, they get saved in a file called 'iTunes Music Library.xml' which links itself to a computer or user on a computer, so the playcounts are unique to computer, not the song file itself. In other words, when you copy songs from one library to another (even if you put it dirctly in the iTunes library folder in 'Music') the playcount doesn't carry accross with them.
There may be some small apps out there which overcome this, but i've not seen any.
Sorry!
Tom