I've got some shares on a mythbuntu machine that are set up thus:
[music]
comment = music on mythtv box
path = /media/music
read only = No
public = yes
writeable = yes
printable = yes
I can see them on my OSX laptop and if I look at the permissions it says I have read/write access, but when I try to write to the share I get an error saying that the file is locked or on a locked volume.
I have recently wiped the ubuntu OS partition and reinstalled, these shares are on a separate drive from my OS which weren't touched in the install. I had to manually edit fstab to mount them, so that could be another source of problems. However I have chown-ed them all to my ubuntu user account and on the mythtv machine they are all readable and writeable on the ubuntu machine.
As a side question, what is the difference between read only = no and writeable = yes, or indeed public in smb.conf?