[Leftos]

Like clipperfan811 said, make sure your motherboard supports the upgrade to the i3 processor. I'm just basing my not recommending you should buy a new one on your current CPU, which I would fare to guess is a 1755 socket, so the i3 processor should be compatible.

You should also make sure that you get a decent 450W PSU, not the cheapest one there, because some may say 450W on the label, but the most of the juice they can get out can be all too little for your new components. Your i3 shouldn't tax the system much power-wise, but depending on what GPU you get, you might want to make sure you throw some extra money on the PSU.

Also, I might add that 450W is a proper wattage for the system I've just suggested and the one I have currently, but it doesn't give you much room upgrade-wise, unless you dig deep to find really power-efficient components.