How to mount an NTFS filesystem, allowing all users full access?

From man mount:

Mount options for ntfs

            ︙
uid=value, gid=value and umask=value

Set the file permission on the filesystem. The umask value is given in octal. By default, the files are owned by root and not readable by somebody else.

So you should be able to do what you're after with something like

mount -t ntfs -o umask=000 /dev/sda1 /media/drive

which should give everyone read and write permissions on the volume.