do you have permissions for /mnt/net? i have a similar problem here, except when i try to mount the samba server's shared drive to a pcbsd computer, it asks for my password, but pressing enter will do just fine;
also, i can't mount the drive during startup, because it stops and waits for me to press enter, and does nothing, but i can make a simple script that runs when kde starts, so i have it mounted when the desktop appears:
mount -t smbfs //server/samba ~/server #
#as it is here
the final line has an extra 'enter' at the end of the line, so when it asks for the password, the empty line comes and tells that it's an empty password.
it worls for me. of course, the ~/server has full permissions (drwxrwxrwx).