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I use "Jump" to connect to my Windows 7 Ultimate at work.

It's not so much the remote desktop application that you have to worry about - you need a VPN connection to make it secure, or use one of the remote access products like GoToMyPC (I'm assuming they have an iPad add available - I don't use it so I'm not sure).
 
Install VNC.

Microsoft disabled its remote control feature (and other features) on Home versions of windows
 
I use Desktop Coonect on the iPad and TightVNC (which is freee) on Windows7 Home Premium ... works well.
 
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