Windows Vista Home Basic Activation Key error

I am using an old Lenovo (IBM) T40p Thinkpad and have installed Windows Vista Home Basic on it. The disc has a Key and I have repeatedly tried to activate the OS using this key but it always gives me this error
0xC004E003.

I googled this and was directed to a site for a registry cleaner (Little Registry Cleaner) which I installed and used to scan my laptop with. It found some errors and repaired them, but the error still occurs. I also read on some other sites that it really does have to do with the registry.

Questions:
How can I fix this (if at all)?
If I don't fix it, will Windows really stop working (I ask because it says it COULD stop working, not that it definitely will stop).
Hope someone can help me out, thanks.

Try the steps shown here

http://support.microsoft.com/kb/950755