If you block Google Sites from storing cookies you will probably stop Sites from working: you just need to clear cookies and cache when there's an issue, then Sites will create a new copy of cookie it needs.
The only virus I've had is Windows itself. Malware if ever there was such!! :)
Well there two other OSes you can use: Mac OS X (this is my first choice but the expensive route as it requires a Mac) and Linux that I and Google recommend, especially Ubuntu, as it's free and it's what a lot of Google employees use.