You don't install RedSn0w, it's a standalone executable application. You have to check your connection gateway then, because I'm downloading RedSn0w just fine using either of those links. Here's a link for jailbreaking using RedSn0w. Just change the IPSW that you're selecting to the iOS 4.2.1 IPSW for the 3G. Ignore the Booting Tethered portion at the bottom
Create a DFU IPSW to use with iTunes. Go to Extras > Even More > DFU IPSW, select the iOS 4.2.1 IPSW. RedSn0w will create a ENTER_DFU_iPhone2,1_4.2.1.xxxxxx.IPSW. Open up iTunes, shift+click Restore and point it to this new DFU IPSW. Let the restore process go through. At the end of it, you'll be in DFU mode. Once you're in DFU mode, follow the guide, except you ignore the parts where it says to put the device into DFU mode since you're already in DFU mode.
You select the iOS 4.2.1 IPSW for the 3G...........
You should still have access to your device regardless of whether you've activated or not. Otherwise, open up Assistive Touch in Settings.app > General > Accessibility > AssistiveTouch > On. Then use AssistiveTouch to turn your phone off while it's unplugged. While it's off and unplugged, hold the home button down and plug it in. Keep holding the home button until you see the Recovery Mode screen. Now go to iTunes, shift+click the Restore button, point it to the DFU IPSW that you created, let it DFU your device, then follow the instructions.
i dont have any access to my iphone that picture is what pops up when i press the home button, then i slide it and i get the emergency call option when i try to get out of it, it goes back to the same image in the pic i put up, i cant get into anything on it from the phone, does it make sense i can touch the i with the circle on it and i get an IMEI number and a ICCID which says unknown under it but thats all i can get to, no clue why