The fuse box in most cars and INCLUDING my 98 infiniti q45 is located by the feet of the driver. For the Q45 it is to the left of the parking brake. Look and you will see only one hatch covering the fuse box. It is also shown in your Manual.
An excellent answer (with step-by-step instructions) can be found on the Nico Club site. This club is composed of owners of Nissan and Infiniti cars. The post related to replacing the starter on 1991-1995 Q45's may be accessed @....... http://forums.nicoclub.com/zerothread?id=120220