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You can get something like Splashtop that lets you mirror and control your computer over wifi, but there is no way currently to actually run windows on the iPad itself.
 
How to run windows on the iPad2

I have a set of apps called on live viewer and on live desktop. The desktop allows you to run windows as a part of the set. The viewer is like a game application that allows you to play online games with other people. You need both of the apps in order to get the desktop app to work. You might want to look into that. I am not sure if the price is still 0.99 cents. The app works okay but you have to log on to the site in order to run windows and that can take few minutes sometimes. I hope that this is of some help to you.
 
There was a way to run older versions of Windows natively with the iDOS app, but that app was long ago pulled from the AppStore. Currently, viewing a remote Windows box as the others have posted is the only way unless iDOS or some other DOSBox-based emulator is available for jailbroken iPads.
 
The way I do it is through Citrix Receiver. It's good for sending my work emails and reviewing documents but nothing more intensive than that imo.
 
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