Well as far as I know the landclass format is very similar between the 2.
The only thing is that FS2004 *might* have some new landclasses not supported by FS2002. The only real way is to compare the information in the 2002 and 2004 sdks.
I do know that the FS2002 sdk tools create files that will work in FS2004. Whether the reverse is true I can`t say for sure.