Here is an example i found :
<Anonymous your_directory>
   ...
   ...
  <Directory incoming>
    <Limit RMD DELE SITE_CHMOD RNFR>
      DenyAll
    </Limit>
    <Limit CWD MKD STOR RETR STAT>
      AllowAll
    </Limit>
  </Directory>
  <Directory incoming/*/*>
    <Limit MKD RNFR DELE RMD SITE_CHMOD>
      DenyAll
    </Limit>
    <Limit CWD RETR STAT>
      AllowAll
    </Limit>
  </Directory>
</anonymous>
#Okay, all of the mess above is really pretty simple.  The first Limit 
#directive says "You can't remove files or directories in /incoming."  
#The second Limit permits users to create directories, change into them, 
#and up/download files to or from this directory or any created in it.
#The third Limit says that in directories created _in_ /incoming, you may not
#create any more directories, nor as before, remove files or directories.  The
#final Limit statement says that it is fine to change into directories created
#in /incoming and also to download files from them.
Remember, it's an example. I never test it on SME.