Outlook Express used to be a major source of transmission for viruses. While these seem to have tapered off recently, it's still not a very good mail client. Once again, a better alternative exists in the form of Mozilla Thunderbird.
Thunderbird, like Firefox, is a small, free, lightweight and secure mail client available for Windows, Mac OSX and Linux. It supports multiple profiles, so the whole family can use it. It also supports multiple accounts (IMAP and POP3.) I use both Firefox and Thunderbird on all of my PCs. They are great programs.
If you have high-speed, please buy a DSL/Cable router. They are worth their weight in gold, as they add a layer between you and the Internet, have a built-in hardware firewall, and allow you to connect multiple PCs. As a bonus, they also make it so that you don't have to use Sympatico's crappy Access Manager, as the router handles the authentication. A decent router, with wireless, is less than $100. Buy one, you won't regret it.
If, for whatever reason, you refuse or are unable to buy a router, use a firewall. If you're running Windows XP, make sure that you have installed Service Pack 2 and have enabled the built-in firewall. If you're running a pervious version of Windows, install ZoneAlarm. Please note that you DO NOT NEED TO UPGRADE TO THE PRO VERSION OF ZoneAlarm. The free version works great and will continue to work well for you. Also, don't worry about port scans or other things that ZoneAlarm mentions to scare you into upgrading. These things happen and are often misreported/misleadingly reported by the firewall companies.
Finally, please avoid Symantec's firewall. It seems to behave very strangely and tends to cause at least as many headaches as it solves. Their anti-virus program is decent, their firewall is the pits.
E-mail scams, popups and too-good-to-be-true offers are everywhere on the internet. Peer to Peer programs are often bundled with malware, the files on these networks are often not what they seem. If something seems just too good to pass up, it's probably bogus. If someone sends you an attachment, mail them to make sure it's legitimate before you open it. Malware often hides itself as an image or movie file. Think before you click.