It is possible to configure the mouse for FPS games using N-Rage's input pulgin. There is a problem though. The way the N64 joystick works causes the games to not quite feel right with the mouse. Some games are more affected by this than others. Perfect Dark, for example, feels more like a real PC game than Turok 2(turn lookspring off in the Options menu in Turok 2 or else looking up/down becomes a HUGE pain), however both don't feel exactly like a PC game(You can't instantly turn around like you can in Quake 3, and the mouse will feel like it has 2 or 3 "speeds" instead of the nice fluid motion you get in a PC game).
To use the mouse in N-Rage's plugin, click the big "Assign Keys" button, (I use ASWD buttons for moving) then in the top right corner, select mouse. In the left column, there should be a group of buttons inside a box called "Analog Stick". Click the direction for the stick (e.g. "Up") and move the mouse in that direction. Repeat for the remaining three directions. Next you assign the movement keys (in most N64 games these are the C-Buttons) in the same manner, but you should use the W,A,D,S keys (Or any 4 keys) instead of MouseUp,MouseLeft,MouseRight, and MouseDown. Assign Left click to Z, Right click to B, Middle click(if you have it, if not, make it an easy key to reach, if you use my config, E works nicely) to A, Space to R, Q to L, Enter to Start, and the arrow keys to the D-Pad.
Hope that points you in the right direction.
