Play L.A Meltdown and take it slowly killing everything you run into. Check every secret area for enemies. Make sure you go past or in the dumpster at the start in the streets and jump through the seats in the theatre to spawn the enemies there. at the end use the jetpack to go all the way up to the top and shoot the two turrets near the end level.
There are 26 total, the two hardest to find are the turrets, to check your total, quicksave [F6] hit the end level, it'll tell you, then quickload [F9]
The secrets are here
http://dukenukem.wikia.com/wiki/Hollywood_Holocaust*** Spoiler - click to reveal ***1.In the street, jump up onto the crate, jump onto the sloped ledge, and then jump onto the higher ledge that crosses the road (underneath the "Innocent?" sign).
From the sloped ledge in Secret 1, jump into the building through the second or third window from the right. You'll arrive in an L-shaped room, with a small bed with a box of RPG ammo on it. That RPG ammo is the second secret.
Inside Secret 2, use the "Biker Bimbos" movie poster at the far end of the room to reveal some Steroids.
In the lobby, use the cash register to open a hidden room high up in one of the walls of the lobby (to the right as you're standing behind the snack bar looking out). Stand underneath the hole and use the wall. A hidden platform will raise you up to the room, in which you'll find some Armor.
In the projection room, use the brick wall next to the fire extinguisher near the stairs. (You can also get there through the vent leading from the bathroom.)
In the projection room, jump up onto the projector to open a hidden area of that room.
Open the curtains of the cinema screen (the switch is in the projection room), and blow up the crack in the screen to reveal a hidden area behind the screen.
In the street, one of the windows next to the cinema sign leads to a hidden room. Either jump (from the tree) or fly into it.
A video guide for those who want one