The first prerequisite to be able to run VoxCommando (version 1) is that you must be able to run Windows speech recognition, since it is built upon the same engine. If you can't run Windows speech recognition then you won't be able to get VC to work either.
If you only have En-GB installed then I thought you would still be able to get speech recognition working, but I'm not sure.
Which version of Windows 7 do you have? I recommend that you install the full language packs for En-US and En-GB if you need that. On Windows 7 Ultimate this can be done very easily using Windows Update:
http://windows.microsoft.com/en-ca/windows/downloads/install-languages-with-windows-updateIt is important to note that there are two types of language packs. There is just the small version which includes translations of text for windows menus, buttons, etc. These packs are available for many languages.
Then there are the full blown language packs that include the speech recognition stuff. These are only available for some languages. (English US+GB, Spanish, French, German, Chinese, Japanese).
If you don't have Windows 7 Ultimate then there are some unofficial workarounds that allow you to install the full language packs. I believe all version of Windows 8 have this option.
VC2 (when it is released) will allow you to use a different speech engine which can be downloaded to any Win 7 machine, but which has different characteristics than the "desktop" based speech engine.
If you are able to get speech recognition running on Windows and you are still having problems getting VC to work we will solve that problem later.