Can't imagine English prices are too different to Oz prices, so agree with Evo that your 600-700 quid is way over the top for what you want. If you're not interested in high-end graphics, the cheapest entry level desktop these days is going to do everything you want. Buy it from your local reputable dealer so there are no problems with service, and you can't go wrong really.
Don't accept less than 512Mb RAM, and there is no need to accept a CRT monitor either. Flat screens are the default now.
Entry level laptops here are now the equivalent of 400 quid, so a basic desktop should be less than that with all the features you need.