Re: "The following updates were not installed: Security Update for Microsoft .NET ...
I am assuming that you have administrative privileges and that you have enough disk space. Also, you might check to make sure that a spyware/anti-virus program is not blocking the install.
How are you updating? clicking the icon in the sys-tool bar? if so, then open up IE, and click Tools, then windows update, try using that instead.
If this doesn't work, then try and find a Manual update.
Note this is just basically repeating what I said in another forum, but it is a good start.