Go through the first level of the NPP and drop enemies as you go. Your goal is
to find the stairs to the next level up -- the enemies here are hard with the
Tunder, but they are not too far off your gun is useless. Just make two quick
saves judiciously and you'll be fine.
At the top of the stairs, you can go towards left for the Wishmaker (note any
interaction with it will end the game with a "fasle ending"),
or go right and
look for a side shaft with a ladder leading up. Both sides have about 20
enemies (the hallway loops around), so if you decide to go one way, you can
try to get to either the Wishmaker (no enemies there, and a lot of radiation)
or
go up the ladder (enemies cannot use ladders in this game).