Be careful with 'Branded' Computers (HP Dell Compaq) The desktops have very limited expansion options, your basically stuck with what you get. They tend to use motherboards with the graphics card built into them, expanded with a plugin memory module.
The specs on the 2nd machines look better, but it has onboard graphics, which means if you ever want to change the graphics, your looking at a new motherboard.
If your shopping on trademe your'd be looking for a
pc description like this one This pc is also around a price you'd want to pay for a gaming pc, anything under a $1000 is either a very good deal or a very bad computer dressed up as a very good deal.
It lists all the components, so you can see who makes the parts, and you even look then up on the internet for the actual tech specs and reviews.
Something else to watch is the wattage of the power supplies, some of the pc's come with a power supply that is underrated and will go pop on you, the one i posted is sus, 300 watts is a little light these days.
Sorry for the longish reply, hate seeing people buy these 'special deals' from retailers only to end up with a lemon.