I've done a lot of reading on this over the past day to get this working. It seems that there are two common problems keeping this from working for most people.
1.) directory permissions:
The user you want to have rw access to your smaba mount needs to have rw access to your mount point.
First, unmount the smb share. You cannot change the permissions of a mount point while a share is mounted to it.
You can either change the directory permissions by opening up the mount point to everyone
chmod 777 /mnt/yourMountHere
or by changing the group of the mount point to a group that your user is in.
chgrp yourUser /mnt/yourMountHere
chmod g+rwx /mnt/yourMountHere
Test this by changing to the user you want to write to the share as, then cd to the mount point (whille still unmounted) and try to create a file. You should now be able to, showing that your permissions on the linux side of things are OK.
2.) uid and gid settings:
Now you need to be sure that your fstab has the correct settings to allow that user to read and write to the mounted dir.
Here's my fstab entry
//serversus/Albums /mnt/albums smbfs username=administrator,password=xxxxxxxxxx,uid=500,gid=500 0 0
Where the uid and gid pertain to the user and group I want to have access to the share. You can see your uid and gid for each user with the command