How to trick windows 7 to use only a part of the screen [duplicate]
Based on my comments I think this deserve's its own answer.
Create a toolbar
Drag it to the top of the screen and make it as big as you need.
And finally make sure it is "Always on Top"
Simple solution that doesn't require any additional software.
I've found a program called DesktopCoral which do a similar thing as in the links toolbar but actually works in Windows 7. Still don't have an idea how to limit the cursor position.