lock user to directory in ftp

how can i lock a specific user to his home directory when he logs on to the computer with ftp?

thanx!

check if chroot can be implemented. Probably this might be useful

i thought about chroot...
can you give some information about it?

ohh and another thing...
i dont give the user a shell...
so the solution needs to be for FTP only no use to try "rksh"

thanx again...