Yes it does give you Siri
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.
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.
It is up to you. No matter what you have on your ipod will become messed up when Jailbreaking...
As of today (November 24th, 2010), jailbreaking an iPod Touch is not illegal. Is it 100% safe? No.
Jailbreaking an iPod could either be a success or a failure (meaning your iPod could break). It's your decision, but a risky one.
I think that many people are finding the most jailbreaking software for their ipod.
Yes, jailbreaking does void the warranty.
Yes
It is illegal.
no
you cant
jailbreaking the ipod touch is legal. But if you use the tool that gives you all apps free it is illegal.