How to Jailbreak ipad software 4.2.1

Download the redsn0w software Redsnow b4
Upgrade to iTunes 10.1 if you haven't already.
Install the iOS 4.2.1 firmware via iTunes as usual.
Run the redsn0w software executable.
Redsn0w will ask you to select your IPSW file for your current firmware. Point it to one of the following, depending on your OS:
Mac OS X: /~/Library/iTunes/iPad Software Updates (or iPhone/iPod Software Updates, as the case may be)
Windows 7 or Vista: C:\[username]\AppData\Roaming\Apple Computer\iTunes\iPad Software Updates (or iPhone/iPod Software Updates)
Windows XP: C:\Documents and Settings\[username]\Application Data\Apple Computer\iTunes\iPad Software Updates (or iPhone/iPod Software Updates)

Redsn0w should now say that the IPSW file was successfully identified. On the following screen, check "Install Cydia" then click "Next."
With the iOS device powered off and plugged into the computer, click "Next" again.
Redsn0w will now provide instructions on how to put your device into DFU mode. This is a combination of key presses, that are as follows: Hold the Power button for 1 second, then without releasing it, hold the Home button for 10 seconds. Finally, release Power but keep holding Home for 15 seconds.
One in DFU mode, the jailbreak will proceed automatically.

Compatibility notes: This jailbreak works on all devices. On iPhone 4, iPod Touch 3 and 4, iPad and iPod Touch 2 (MC model) it will be tethered. On iPhone 3G, iPhone 3GS (older bootroom), and iPod Touch 2 (older model) it's not tethered. iPhone unlockers should NOT jailbreak!

As always, please proceed with jailbreaking at your own risk. Although relatively easy, it is a form of hacking and things can go wrong, break, crash or just not work at all. Back up your iOS device before jailbreaking in case you need to restore and make sure that critical data (contacts, notes, etc.) is also safely stored elsewhere than on your PC.

And after that don't forget to install the installous in your ipad so you can obtain game or apps on your ipad here are the steps:
1)Go to Cydia.
2)Go to Source.
3)Click add.
4)type cydia.hackulo.us
5)Click add.
6)Go to the Hackulo on the screen at the cydia.
7)Click the Installous and download it.

Thx...