Trojan.Virtualroot Virus

Hello. I just received an alert that computer was infected with Trojan.virtualroot virus.. tried to quarantine infected file. no luck.. tried to delete…said file was in use or cannot be deleted from windows. Name of file explorer.exe .. in C: root directory.. file is like 8kb.. NOT the file that normally resides in WIN directory on this win2000 machine. Any suggestions, please?