it depends on what firmware u have..
if its 3.0 then download redsn0w from here http://www.aboutonlinetips.com/download-redsn0w-to-jailbreak-iphone-os-3/
then open it.. browse the firmware, switch off ur iPod touch, click next.. follow the instructions.. its too easy!!
if its 2.2.1 then download quickfreedom from http://quickfreedom.com/ then open it n follow the instructions.. if its 2.2 or lesser that download quickpwn at http://quickpwn.com/ if u need any help then feel free to email me!
edit: hey if its 3.0, then download redsn0w 0.7.2 from here
http://www.blogsdna.com/3762/download-redsn0w-072-for-windows-mac.htm
the link i gave before was for 0.7.1! dint know that the new one was out! will jailbreak mine again n ll tell ya if it works!
hey if its on 2.2.1 then u need to download libusb too.. here is the link: http://www.linuxfromscratch.org/blfs/view/stable/general/libusb.html remember, if u r on vista, then after installing libusb, go to its properties, then under compatibility tab, run it in compatibilty mode for XP.. this is very important otherwise ur iPod wont be connected!
edit: u will hv problems wid cydia on 3.0.. it aint upgrading.. but if u jailbreak with redsn0w 0.7.2 then u can get icy too.. use it as an alternative until a betta jailbreak comes!