First, purchase and install anti-virus software. Names like Norton and McAfee and a handful of others produce good products in this category. Part two of this resolution is to tighten up your own security procedures, especially when it comes to e-mail. Also pay attention to the icons on your file attachments. And if you ever have any doubts about an attachment, simply reply to the sender and ask if they really sent the file.
Security goes beyond e-mail, too.
If you'd rather leave it to the experts, buy some good firewall software instead. Symantec's Norton Internet Security, Family Edition, is nice for the home because it also includes filtering software that you can use if you want. You must be prepared to keep it after that month is over, because I can guarantee you won't want to go back to your analog modem. With cable or DSL, the Internet becomes a real tool that is always ready at your command, not just something you use when you have the time to dial the modem and then wait for glacially slow downloads. I mean, rolling out of your computer chair funny.