As far as I am aware, the nvidia 6200 does not actually have 256mb of onboard memory; Instead it has 64mb of onboard "Turbocache" and uses the main system memory (up to 256mb) as a framebuffer. It's not that good a card anyways, and would only appear to offer similiar performance to the past generation of cards, but at a budget price.
The Aldi system looks a half decent buy otherwise, and if you throw a £60 Geforce 6600 256mb in there, it'll offer decent punch. A similiar AMD system could be built however, running cooler and quieter, for around £500. If I bought the Aldi system, I'd throw in new graphics because you wont see much of a performance boost with the Turbocache 6200's.