If you are looking to jailbreak an A4 device: iPad 1, iPhone 3GS and iPhone 4. You can use a more RELIABLE technic by apple a tethered jailbreak first with Redsnow and then installing the un-tether package via Cydia which is exactly what Absinthe does, but just in a slightly different way.
1. Jailbreak tethered with latest version of redsn0w. By clicking the jailbreak button and then you need to install Cydia when prompted
2. Once Redsn0w has run and finished on you phone.
3. In redsn0w, go to extras and then use the just boot tethered now option.
4. Once booted, locate Cydia on your iPhone. Open and let if finish loading all the packages up the top (this isn't required every time you open Cydia, just the first.
5. Then go to search and search for 'rocky racoon 5.1.1 untether'.
6. Install this and then reboot your phone, by switching it off and not by using redsn0w.
7. You are now jailbroken un-tethered.