Yes, just boot from the installer disk and after installation if you have a problem with authentication of your key, call Microsoft. They are understanding and have never given me any problem with the authentication.
I just did a reinstall with my win 7 pro disc after my 80gb hard drive was failing...onto a 250gb one and used the same product key. It activated no problem without having to contact Microsoft. So I say "go for it". Sucks to have a partitioning error. Good luck.
I have tried this, but when starting up, windows says BOOTMGR is missing. What do I do about this?
Start you own thread and you are far more likely to get an answer to your problem -- include details of what you have done so far and the specific problem. Very few folks will see this post at the end of another thread.