Trojan Horse removal help request

Today, stupidly, I opened an attachment. Immediately my Norton Anti Virus told me I had a Trojan Horse. I ran a complete computer scan with Norton but nothing came up. I went to the activity log where I found two lines saying I had a Trojan Horse in my C;Windows\system32\wiPK.exe file. One line said that the delete failed, the other line said "access denied". Can someone help me get rid of this Trojan Horse. I know it must be more complicated that picking a system restore point prior to the infection. I'm running XP Home. Thanks

 

I just loaded AVG and ran it and it says "no threat detected". But the Trojan Horse is still in the report from Norton. I can't look at the file C:Windows\system32\wiPK because it's a Windows operating file. Any help would be appreciated

 

I just went through explorer and could not find the offending file C:windows\system32\wipk.exe under the system32 folder. Does anyone have any idea on what's going on??????????