Two thoughts. The first is why don't you just try changing the language settings on your existing installation ? As I remember, if you use a Windows repair disc the first thing you are asked is to choose your language and keyboard. You can get full instructions on how to create a Windows repair disc here :
No guarrantees it will work, but if it does it saves you a lot of work !
I have Win 7 Home Premium and the complete Windows folder is 27 Gb. This is quite a lot, but I am surprised that you are being told you don't have room to install it. I would expect any new laptop to have at least a 250 GB hard drive. But if you are determined to put Win 7 HP on your laptop, I think you are going to have to remove the Pro version first. Just back up any data you have on the computer before you start !