What is the name of the trojan being identified by Symantec?
Have you tried restarting the machine in Safe Mode and than running the scan?
Sounds like the trojan is being loaded into memory and simply removng the file will prove futile, as it is in a process, most likely svchost.exe and thus, whenever the system is restarted it will recreate the file. It probably also has a registry entry in
HKLM/Software/Microsoft/Windows/CurrentVersion/Run or
Runonce or
RunOnceEx
Verify that nothing is in those registry keys that should not be there....