Hi Peter,
When you say "hit by viruses" does that mean your G4 is infected with a virus?
If your concern is that you are getting lots of e-mail that is carrying a virus, then removing your G4 from the Internet isn't going to stop these. When you get the older machine hooked up and collecting e-mail, it will be collecting from the same mailbox the other one was. That mailbox will still be holding those viruses for you. If you actually have a Mac virus, you might get a writeup in the news..
Please clarify what you mean by "hit by.." If you have some of these virus carrying messages where we can see the full headers, then we may be able to discover who is sending them. If it is someone you know, then calling them may help. If it is a stranger, notifying their ISP may help. The SWEN virus is making lots of people angry and some ISP that have turned a blind eye up to this point are beginning to be more proactive and alerting the customers who have infected machines.
see ya