That’s what the iPhone hacker iH8sn0w Said:
Excellent news. Siri is not just compiled specifically for the A5 (s5l8940x) processor
Which means the A5 processor is not the problem and the proof that it’s working on iPhone 4, not working well but it’s possible and we think that the iPhone hackers will take care about that .
Siri On iPad 2 :
Sonny Dickson the iOS developer has announced that he could port Siri in the settings app of the iPad 2. Siri on iPad 2 should be available soon.