Help!

My iPod/iPhone won't sync to iTunes and, when I reinstall it, an error message pops up: "Module C:\Program Files\iTunes\iPodUpdaterExt.dll failed to register. HRESULT -2147024770. Contact your support personnel."

I have tried installing a previous version of iTunes and I still get the same message. I've also followed some steps recommended by Microsoft and it still has given me the same message. How do I get iTunes back to working right again?