One can use a webmail account to receive e-mail. This allows reading and replying to messages on the ISP server and only downloading mesages considered safe. Most ISPs keep up-to-date virus and spam protection as a first line defense.
One can use alternative programs for e-mail and web browsing like Netscape or Mozilla. Most virus are written to take advantage of security problems in InternetExplorer and OutlookExpress. Avoiding IE & OE does not make a system 'virus proof' but rather reduces the vulnerability and risk. It compliments but does not replace AV security programs in our computers.