Say to your parents that whatever there looking to do a custom built pc is alot faster (most of the time) and most probably more stable as there is things installed u wont need e.g. tv tuner card
Vista Ultimate needs alot of power im running it on my computer and its not running as nice as it can.
Like i said companys always find the cheapest Components they can find like the RAM for instance "1GB DDR2 RAM" that means its probably the slowest DDR2 RAM you can find as it doesn't tell you the speed of it.
Pre-built computer wont have DirectX 10 cards for along time yet as because of the companys cutting corners. If you want a computer to play games you can either spend double your money on a pre-built gaming pc or get a custom built computer for a computer store etc.
If you asked for advice about the computer but you are not taking into account the other options being given to you. We are trying to help you as if you buy that computer you will be getting ripped off. My m8 bought a pre-built PC and upgraded it but he spent more on his pc than me and his isnt as fast as mine and he still has a rubbish motherboard.