Open your fstab file using a texteditor. It's located /etc/fstab
Put the group 'users' in the line for your ntfs partition.
It's gonna look something like this:
/dev/hda1 /windows/C ntfs ro,users,gid=users,umask=0002,nls=iso8859-1 0 0
Save & exit.
Now you should be able to access as a regular user.