You can use free software like Greenpois0n, Redsn0w, and Lydia.
Yes, now Greenpois0n can jailbreak iOS 4.2.1.
No you do not put Greenpois0n on an iPod. You install Loader which in turns installs Cydia.
greenpois0n.com
greenpois0n is the best jailbreaker for ios 4.1 on windows that i have used( i have personally used it and it is safe , just beware of fake downloads)
No
It already is for a long time
it has but not for the iphone 4
Of course...by restoring the ipod.
It is a matter of opinion, in my opinion Greenpois0n is better because that is what i used to jailbrake my ipod touch 2nd generation 4.2.1 ... do NOT use jailbrakeme.com that is just a virus and it brakes your ipod.
it takes a few minutes by the handsome jevon landsmark
Yes. I recommend the greenpois0n jailbreak, at greenpois0n.com