Vista Error Code 646 and 900

Hello,
I have been trying to update my computer for weeks. Well every time I try to install the updates it will go through the process but at the end it will say update failure.The error codes 646 and 900 will show up. There are some microsoft updates as well as service pack 1. I want to upgrade my computer to Windows 7, but it keeps saying I need service pack 1. Please help me I am ready to throw my computer into a wall.

1.Reset WU components in aggressive mode How do I reset Windows Update components?
2.Download & install SP1 from Microsoft Download Center (not from Windows Update) in safe mode

How do I get my computer into safe mode