Thinking of buying a new computer here are a few things to think of when buying a new computer.
Most of these rules should stand for you if your buying one or fifty machines, price will just vary and people you talk to. I am not going to really mention spesific specs since hardware changes so much.
Light weight laptops, they are just small laptops between 8″ and 11″ screens.
They are very light weight and perfect for just surfing the internet on the go.
Most run Linux so lots of free software available
Small keyboard (most people get use to it) smaller the screen the smaller the keyboard.
Not a lot of computing power
Depending on what you get 4/8gb version or 160gb there is not a lot of storage space for music and video.
Larger laptop between 14.5″ and 17″ laptop.
Quit a bit of power
Bit more expensive than netbooks and desktops
Large computer that sits under desk
Options are Tower case or Desktop, depending where you need to put computer if its on desk, on group or in the cupboard size may be an issue.
Cheap for the amount of power you get for them.
Easy to upgrade
Longer life span than laptops and netbooks
Large screen/Large keyboard
Not very portable
Need a dedicated space to put the machine.
Buying from the likes of ebay and buy and sell is not a good idea unless you really know what your doing or getting few replacement parts.
Places I recommend to buy from would be from dell, do not buy any of there extras software etc.. Same with the likes of PC world or Harvie Normans.