Not sure exactly what processor that is, something like the 2410M?
But the 750Ti is a powerful card (For low end PCs), even for the size, and practically any computer would be able to run that card. I believe, on your system there are other upgrades that could happen, this could be to minimize your bottlenecking with the card (If in heavy use)
Such as another 4GB of DDR3 Ram.
But the 450W PSU will be enough for it, and the CPU should be a decent match with it, although second generation is not sold widely anymore, and it would be much better to upgrade that to a more recent generation, but that may be out of your budget, if you have one.