Can you download 3rd party apps to an i pod touch 4th gen running IOS 4.3.1 without jail breaking?

i had heard that you could some how use the SDK to download "cracked" 3rd party apps is that possible? if so how do you do it? If not is there any way to download 3rd party apps on an ipod touch 4th gen running IOS 4.3.1 without jailbreaking?