explorer.exe and winlogon.exe are infected with virus...help

Hello,

Need some help on getting these viruses removed from Windows XP Pro Sp3.
Avirus reports:

explorer.exe and winlogon.exe is infected with TR/Patched.gen. And that
svchost.exe is infected with TR/Agent.szqf.

Ran Malwarebytes and Superantivirus scans. They cleaned some viruses off
system but do not detect the ones mentioned above that Avirus Realtime
Protection keeps saying exist on my computer.

If I just replaced these files from c:\i386 will Windows still boot up OK?

Thanks
Rocky