lookup BeOS, it's probably the most Amiga like OS there is. It'll do everything you mentioned.
It's available as "Zeta" these days but you'll need to pay for it.
There is a free version of BeOS out there if you want to try it, there's also "BeOSMax" which is also free.
I've read too many horror stories and seen too many ruined computers to dream of putting a Windows machine on the net. (Last week a friend of mine had their computer knackered and they were using Firefox which I thought was secure.)
Firefox is secure, Windows isn't.
