Yes, you are going to have to reinstall. However, you won't be able to use build 7000, as that is about to expire. Instead, you will need to install the RC version which is officially build 7100. You can still get this (and the associated key) here Windows 7 Release Candidate
This comes in the form of a .iso file, which you should burn to a DVD using a suitable program in exactly the same way as you did with build 7000.