Are you virus and spyware free? Last machine I cleaned had that exact same problem, and it would only regenerate itself after I removed it from the startup list.
Get SpyBot Search and Destroy (which you should have anyway) and install it. If you go to advanced mode and look under tools, you'll find startup section where you can delete whatever startup entries you want.
However, the problem is more of why this started happening. Windows doesn't just do stuff like that on it's own.
