Are you limited to those three specific CPUs? AMD is about to cut prices, and the X2 6000+ will be $159. That's some serious bang for your buck, and worth every penny over the 4400+.

Right now, I believe that the Core 2 Duo's are the better CPU on the market. They're cheap (that E6420 is like $200 USD I believe) and they use little power and can overclock well.

AMD all the way.

Right now, Intel Core 2 Duo leads.

Right now, Intel Core 2 Duo

I would have said AMD if you'd asked me just over a year ago, but since Intel dumped their P4 Netburst Architecture and continued with their PIII -> P-M -> Core path, they've actually turned things around quiet significantly.

It all depends on what 'general purpose' computing actually is. If you are referring to something that edits office documents and surfs the web, you don't need much. If general purpose includes Video/Audio editing, development, Modelling/Animation, etc... then you'll need something more powerful.

If you want something for gaming, as previously mentioned, you'll be limited by your video card more than your CPU unless you plan on spending AU$500+ on an 8800.

In regards to upgrading, in three years time you'll possibly need to buy most of a new system anyhow, so it would be better to spend the extra on CPU rather than RAM at the moment, because dropping some more RAM into the system at a future date is usually cheaper than upgrading the CPU (plus, 2GB of RAM should be more than enough for general computing).

AMD and use the extra $$$ to get a good GPU (Get one 8800 GTS or X2900XT)