@adwsys, this is how I have configured my 12.04 servers so my Windows 7 PC can write files to the server.
The differences between yours and my config files are the following:
Comment out those lines and see if you can access (and create files).
username map = /etc/samba/smbusers
public = yes
guest ok = no
writable = yes
directory mask = 0777
If not, then check your /var/www ownership and permissions for discrepancies....or create a /srv/samba/share folder and test there to avoid messing with your www files-n-folders.
Once you have it working, then move on from there.
It will work, you just have to figure out what you are doing that is preventing from working.