each time i open an excel attachment or a file from outlook 2003.it is recognized as a virus
Outlook does not have any virus detection capability by itself. Please read the message again carefully. It is a virus only if the message is from an antivirus program.
Although you haven't bothered to post the message here, I guess it is telling you that the opened file is dangerous and may contain viruses. There is a setting in Outlook options that lets you open this kind of files.