As long as you haven't changed the motherboard you can do a clean reinstall by booting to the upgrade CD.
You can find more information in regards to the different versions of Windows 7 HERE
Thank you for your reply and the link to the post above. I could not find any information under the upgrade version of Windows 7 that states I can do what you said though. I will not have a chance to "go back" in any way so need to be sure (hope you don't misunderstand) as I will be using Darik's Boot and N to clear the data on it... So you are saying that if there are no hardware changes, I am good to go and the upgrade disc will work after inserting the disc after I have wiped the drive clean?
(It does say that my new licence is valid and the old one no longer works (which means that I cannot use the Vista key printed on the underside of my laptop anymore to re-install Vista and then upgrade to Win 7) but it also says that I can move my Win 7 upgrade licence to another computer as well... )