Trojan:DOS/Alureon.A in windows xp?

My computer is redirecting me like crazy. I am using windows xp service pack 3. I am running AVG antivirus and Malaware megabytes for spyware. I ran a Microsoft Malicious Removal Tool and it keeps coming up with this Trojan:DOS/Alureon.A. It's confusing as my virus and spyware are not picking it up. I do not have the original windows xp install as I have had this computer a long time. I also am not able to update to windows seven can anyone help?