This is one of my favourites, a quite interesting and complex level. Leave the cave through a building and destroy the turrets on the surface to deactivate the supply hangar forcefield. Inside the hangar you'll get the G1-key and some goodies, there's also the (useless) Guidebot fire extinguisher under the ceiling. Go down into the caves but watch out for the new Thiefbot to attack you. Explore the caves a little bit to find 2 secret areas the first of which is directly in the cave under the hangar. You'll find some Missiles and even the Vauss in the second cave.

entering the prison complex

You'll eventually enter the prison complex through the yellow tube. Besides another key you'll find the forcefield blocked entrance to the Minimum Security Level here. Before you use the G-1 key check the tubes in the adjacent room for more goodies. To deactivate the forcefield simply place yourself in the niche right of it whereas you see the forcefield you want to open in front of you and the other forcefield (with a Tubbs behind) on your left. Now cycle through your keys and use the right one; check your config on which keys are bound to cycle inventory and use item. Gwar gave me the hint that getting the right key does not involve real guesswork.

You got to collect several passkeys to gain access to the various security levels; remember the key sequences in D1/D2 ;)
BTW, Jason Leighton mentioned on the DBB that the X-1 key was only put in to throw you off, it's not needed for anything!

rescue Dr. Sweitzer

You have to create a diversion to make Dr. Sweitzer get shifted to a lower securtiy level so that he can be picked up. Check the maximum security level for a locked service tunnel. Shoot the grate and follow the tunnel to your right. You'll come out in a room with two switches; shoot the left one to produce a small chemical ball which in turn will be picked up by a drone. As soon as the drone is over the acid pool, shoot the right switch to get rid of it. The chemical drops into the acid and explodes causing an evacuation program that causes Dr. Sweitzer to become shifted to the lowest security level. You just go to locate his cell (see my map screenshot above) and then fly atop the level to shoot a trigger which deactivates the forcefield so the shuttle waiting outside can evacuate him.

BTW, it is a known bug that with some ATI RAGE PRO TURBO AGP graphic boards (and even some others) you can't look through the partially transparent glass windows which in this case prevents you from getting on with the level as you can't smash the glass at all (you can do it in other levels though). Outrage put a workaround in the 1.1 patch: open the D3 launcher and go to setup | misc | optional D3 command line switches and add -NoRenderWindows so that those windows become fully transparent. Alternatively you can count about 15-20 seconds before hitting the second switch and the alarm will go off.

destroy all prison records databanks

This is only a secondary objective and thus not necessary to finish the level. In case you wanna do it be sure to check out *both* rooms with the data nodes, they are on the medium security level and close to each other. As well you got to destroy the Novak Prison Records Super-Computer on the maximum security level.