I will add a note to the excellent advice posted above.
The reason you do not want to open attachments, or to leave your Outlook Express enabled to open attachments, is because some attachments are designed to open automatically. If one contains a virus, then you would not be able to catch it before it opened.
If you have virus software installed, you will note that the virus software MAY stop the virus from getting into the computer, but this is a secondary stop gap. The best way is to ensure that your security is turned on as indicated in the post above.
If someone you know sends you an attachment, and you feel it is safe, then of course, turn the security option off long enough to open the attachment. Try to make it a habit to turn the option on again as soon as you open the attachment. Everyone forgets.
Btw, I have been virus-free ever since I purchased Norton Firewall and antivirus. It is good product.
Good luck,
Peabody