Last time I checked the car rental lot was on the northeast side of the entrance road to the main terminal and parking area. That would be on your right shortly after you get off the freeway. This is a somewhat ancient memory since the only time I was actually at the rental lot was several years ago when checking out a used car for sale and I don't normally pay much attention to the rental lot as I drive in. The address for one of the NCR locations on Glumack drive is right where I remember seeing the lot. Glumack Dr. is the name of the entrance road to the main (Lindberg) terminal.
The two locations serve the two separate terminals. MSP is kinda unique in that one terminal complex is well removed from the main group of gates. There's a bus and train going between the two and you can get from one to the other on back roads if you know where you're going but it's almost like two different airports. One terminal complex is called the Humphrey Terminal and historically was only used for big charter outfits but now there are "regular" airlines operating from there. The other, much larger complex is called the Lindberg Terminal. There's been a recent brouhaha over a plan (now going into effect) to "rename" the terminals as "Terminal 1" and "Terminal 2" along with a road signage change projected to cost over a million bucks because a lot of folks have managed to show up at the wrong terminal and missed their flight. Personally I don't think that changing the signs is going to help, probably hurt actually.
