Not that this is the safest way to do it, but you could try something like this. Then, once you have it working, lock it down with tighter security:

security = share 
guest account = publicuser
passdb backend = tdbsam

then

[publicuser]
comment = publicuser Home Dir
path = /home/publicuser
public = yes
writable = yes
write list = +publicuser
browseable = yes
hosts allow = 192.168.10.10

and, in /etc/smbusers

# Unix_name = SMB_name1 SMB_name2 ...
# root = 
publicuser = Administrator smbguest pcguest guest
# nobody = guest pcguest smbguest