Greenpoison if I remember correctly does not work with iOS5. Redsnow is the only tool to tether jailbreak iOS5 for Windows that is, don't know about mac.
fyi there is also Sn0wbreeze for Windows though I much prefer RedSn0w which also works for Mac and PC. Also Pwnage tools for Mac TS use this it will help.
http://www.iclarified.com/jailbreak/
Really? iClarified only had Redsnow but I was jailbreaking from 5.0 not from 4.X so I guess that's the reason I didn't see snowbreeze.