Hi! I've done these steps
1. Install Ubuntu 12.10 quantal (dual boot) specifying mount point for windows partition "/media/win-c". I did it during installation.
Everything works fine with first user: I can access windows drive without any problem.
2. I added a user from default GUI system settings tool. The role was "administrator".
With this user I couldn't access the same drive for not having enough rights. I noticed this user was not member of plugdev group, and my /media/win-c is owned by root user and plugdev group. So:
3. I added the second user to plugdev group
but still I can't access the drive with second user. With root and first user there's no problem. Any idea?