Windows XP Digital Signature error

Hello,

I have been stuck with this issue for over a week and can't find a solution.
I recently had to reinstall a clean version of Windows XP on my HP Pavilion
dv 1000. The operating disk came with the Sp2. Everything went smooth with
installing the operating systgem and reinstallation of drivers but everytime
I try and download ActiveX Control or any other download through microsoft or
other programs I keep getting an error saying "Unknown Publisher" and that
there is a digital signature error. I have tried tweaking my security
options in Internet Explorer 6 but nothing works. Can anyone help me?

THank you.