I have not used the product -  but if I wanted to use the HP as an
FTP server then I would most likely use the third party product FTP/3000 - 
I find the MPE 6.0 offering a little too open for my liking.

FTP/3000 appears to offer the abilty to configure access to the MPE file space on a 
user by user basis. 

In the UK it is distributed by Malcolm Mitchell of Spinner software.  

P.S We've only used the HP as an FTP client - and we've not had any 
major problems - we're obviously not pushing it hard enough. 

(I hope the above wasn't am illegal  <plug> - I declare no interest in the above product 
except that it appears to solve a possible future need.)