Why am I unable to install some apps?
It could mean that your phone does not meet either software or hardware requirements, or both.  You could probably spoof the identity of your phone (so that it could be recognized as Samsung Galaxy S4 for example, instead of HTC Salsa), but you can't expect the app to work properly in this case.

So, I would suggest to get an updated / higher-end phone instead.

UPDATE 2013-10-30: If you're really looking into spoofing the model of your phone, check out Market Helper (needs root).