4g Jailbreak Help Please

[4th time lucky]

Okay when greenpois0n rc5 came out I tried it on my friends 2g mc 4.2.1 on Mac and it failed. I then restored as I didn't no how to fix it. I tried it again an had to restore again. Now I want to jailbreak my iPod Touch 4g 4.2.1
BUT I have 32gb of space and have used atleast 8gb of space. I want to do the jailbreak but do I need to restore and then do it? If I get any errors do I have to restore? Should I do it on the Mac after what happened last time? Help would be great thanks!

[Paco]

Just try it u dont need restore it each time something fails keep trying again but if it a error keeps poping up then tell us what's wrong n mayb someone could help

[4th time lucky]

Sorry, what I meant was I havent tried it on my Ipod touch 4g but was wondering if I do get an error like failed on greenpois0n can I get my Ipod touch out of it without restoring? And if iTunes pops up saying your iPod is in DFU Mode what do I do? Thanks for help but please reply again!