Genuine WinXP Home won’t update

In trying to update this WinXP Home machine from the Windows update page, 15/16 updates failed to download and install. This is a genuine install of the OS, from Gateway.
I tried to install SP2 from the CD, but got the following error message:
“Setup could not verify the integrity of the file: update.inf. Make sure the cryptographic service is running”
How do I investigate the cryptographic service?
Is there a go-around to acquire these updates?