You can in a way if you get open app market and search Siri there is a version there but is is crap
Jailbreak it.
Siri only comes on iPhone 4S and iPod 4S by default and is not installable on any other iDevice unless you jailbreak and install the proper tweaks and packages.
You cannot put themes on an iPod Touch without the jailbreak.
Apple has not currently put Siri on it's iPod Touch. They have released an new iPod Touch that has Siri. This new one is the fifth generation and was released in October 2012. All the old 1-4 generations will not have siri. However, you can jailbreak using jailbreaking software like GreenPois0n, RedSn0w, or JailBreakMe.com. Instructions on how this can be done can be found on YouTube.
Not without erasing the jailbreak.
It depends on what software your ipod is running.
How to jailbreak my iPod touch
you need 4.0.1 to jailbreak it
no, to get a newer jailbreak you have to restore the ipod touch and then update the ipod touch and then download the jailbreak. that is a huge con for jailbreaking.
You can turn off the iPod Touch if you jailbreak it.
No currently there is no jailbreak available for the ipod touch 2nd gen
There is no 3gb on the ipod touch.