Windows XP downloading/installation/digital signatures issue

[Guest]

After recently formatting and re-installing Windows i quickly came accross
the following problem:

When i download something, such as Msn Messenger, Winamp or nVidia Drivers,
upon successful download, a pop up says the digital signatures could not be
verified and am i sure that i want to open this program. i click run or
whatever and it'll either start installing and then stop or won't open at all
and i'll get an error message saying installation cannot be completed because
files are corrupt etc.

Not only is this incredibly annoying and happening to nearly everything i
download, but it seems strange that Digital Signatures could not be verified
for Microsofts own products! Please help, i'm going out of my mind :-s

 

[Roger Abell [MVP]]

Reinstalled XP (while not connected to the network, right?),
and then enabled the firewall and brought the machine up-to-date
on service (pack + patches) ?
Is this the case, that the new XP is up-to-date and known to
have not been exposed on the internet until patched ??
Microsoft Update offers updates for the root certificate servers
listed with the OS after a base istall. Was this accepted for install?