Updating single directory using CVS

[hack_tick]

Hi Guys!

There is a directory "dir_sub" already added and commited on CVS
server, the directory "dir_sub" is sub directory of "dir_main"

The "dir_main" has many sub directory on the CVS server,

Also on my local system there are no sub directories of "dir_main"

I need to update only "dir_sub" from the Repository, so that i dont
have useless data, of other directories

any suggestion??