Can't turn off system restore

My google search results got hijacked, I was getting redirected to "affiliate advertisers".

superanti-spyware found trojan DNSChanger (which caused the problem) and trojan Fake-drop.

But I'm unable to turn off my system restore. I'm concerned one of these infections will return.

I'm running Windows XP.

When I go to my computer, properties, system restore, click on turn off system restore, I get an error message "system restore encountered an error trying to turn off one or more drives, please reboot and try again".

rebooting and trying again doesn't help. trying it on individual drives doesn't help. I have admin permissions.

any ideas?

thanks alot