ISBoxer asks Windows what your CPU's maximum and current are, and if they don't match, it's going to warn you about the throttling. You should have "Power Options" (or some localization) in the Windows 7 control panel regardless of whether you are on a desktop or a laptop. If you can't find the right control panel, type Power Options into the Start menu search box.

It's possible that the "Processor power management" option isn't in the list, but you should still be able to get to the screens shown in the How to disable CPU Throttling in Windows guide.

If none of the above helps, you can check for a throttle in your BIOS but I don't have anything specific to tell you there unless it's a multiplier issue or something.

Either way Windows is reporting that your CPU could be running 50% faster than it is.