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.