You should never reply to any automated emails like that. They are either spam just randomly looking for people that respond (to prove an address is real so they can sell it) or they contain a virus, having been sent by someone else's infected computer.

The only thing you can safely do is delete it, and NEVER open attachments.

If you want to stop spam you need to get a filter, and downloadable programmes don't guarantee to stop spam, neither do the in-built filters in Outlook and Outlook Express.

The only way to eradicate spam is to sign up to a gatekeeper service. This means anyone sending you emails will get a message saying they first have to manually identify themselves as human and not a computer, so it is a bit inhibitive but worth doing to stay safe.
Try these:
http://www.choicemail.com
http://www.mailwiper.com
http://www.mailkey.com
http://www.mailblocker.com