I have an iPod Touch (2nd gen), which can't update past iOS 4.2.1. I can't download many apps anymore, so I was wondering if jailbreaking it would allow me to download the things I want? I don't even mind actually paying for some stuff, it just won't allow me to download it says I need the iOS 4.3 which I can't even upgrade to.
No - we have several related questions, the best phrasing of this problem is here:
The newer software has code the app needs to run, so faking apps out still leaves them crashing when they call the code that only exists in iOS 5 to run.
Jailbreaking won't allow you to upgrade your iOS version at all - those are controlled by Apple, and are dependent on the hardware being used to run them. Your iPod likely doesn't have some capabilities that are needed to run iOS 4.3, and jailbreaking won't change that. Sorry...