Insalleous 4 errors for jailbroken itouch 4g?

Im trying to download real racing 2 -aralon shords and shadow. Im running on ios 4.1 and every download link i pick i download the app but the installation fails invalid ipa i cant download these apps for nothing plz tell me what i can do to fix or u try to get the app and tell me what link u picked or tell me what im doing wrong thanks in advance best answer goes to the method that workd for me