Which Linux Distro installs on a MacBook (13-inch Early 2008) I have a MacBook (13-inch Early 2008) and need to stick with it for some more time, but Apple doesn't give support anymore to it, so I'd like to install an operating system to keep it alive and kicking with low memory usage.

What is your suggestion for a lightweight and compatible operational system for my old MacBook?
How to Test Multiple Linux Distributions

I recommend making a multi-boot USB stick. I used YUMI to create it, and put a number of Linux distros for testing on new machines. You just pick the one to test at boot time, and then you can run it from the USB memory for a while until you decide if it works well on the target machine.

Been a while, but my recollection is that all of the live images were ready to do an install, too. Also can't remember the cost, but I think I paid less than $10 for a large enough memory to hold half a dozen distros, plus state storage.

Recommendation: Ubuntu

My own preference has been Ubuntu these years, though I don't like some of the design decisions they've been making and some versions have been too heavy for my taste. I used one of the Puppy Linux versions for a while, and it was cute and surprisingly robust. Haven't really used Lubuntu that much, but some people recommend it for older and weaker machines.

Probably not relevant to your Mac situation, but I did find one machine that had a weird problem in booting from the USB stick. It was an old ThinkPad, and even though it said it supported USB booting, it didn't work as expected. The trick was to edit the device list to add the USB stick with the hard disk and then move the USB entry to the top of the list before starting. (Unfortunately, that machine was so old and flaky that no Linux was able to cure its WiFi problems... I found a weird WiFi workaround, but too far out of scope here.)