<Would Norton find the virus if I do not open the attachment?

If your settings are correct, Norton should grab the virus even as your e-mail is downloading. In my case, the attachment is hurled into quarantine, and isn't even there anymore when the e-mail finally shows up in the window.

I have also set Norton to check my outgoing e-mails, which protects everyone else, against viruses at least if not against my virulent commentary.

If you are on an "always-on" system, it's also worth checking out a good firewall. I use ZoneAlarm, which is highly recommended, and has the added virtue of being free in its simplest form.