Can I install a ROM made for a different device? I own a MicroMax A100. I want to install the latest version of a different ROM (Samsung or Nexus).

Is it possible? If so, can you tell me how?

If not, can I install a ROM made for a different device, but from the same manufacturer? For example, could I install a ROM for the MicroMax A110, which is the successor of A100?
Short answer:
You can only install ROMs compatible with your device
Longer version
Different Android devices use different hardware, which requires special drivers (e.g. the camera). Those drivers are sometimes/often proprietary (take e.g. Sony, which almost made it into the AOSP project -- but had difficulties due to those proprietary parts and thus had to back-out again: AOSP only allows for non-proprietary, Open Source code, like its name suggests: Android Open Source Project). Installing an incompatible ROM, in the best case, makes components of your device unavailable (they are simply not working). In the worst case, you might &quot;brick&quot; it (it won't even start up).
You might want to check the question Where can I find stock or custom ROMs for my Android device? to find ROMs compatible with your device. Most times, there are several choices available to meet the user's requirements: Less &quot;bloatware&quot; but more performance, more fancy stuff, custom enhancements... So you still can make your pick.
Other recommended readings on this topic:

Are the custom ROM different for different phones?
Is there an official Android “Google” ROM?