The driver displaying Radeon 4800 is normal, for every card there is it lists the base series rather than the actual model of the installed card. The reason behind this is that all of the 4800 series cards are the same card, but the higher model, the more memory/pipelines/clock speeds. The bit where it says Microsoft WDDM is the part where it matters, meaning the drivers come from Microsoft (the most barebones drivers that will work on your graphics card).
So head on over to
www.ati.com and download the drivers for the Radeon 4800 series for windows 7. I would use the driver finder tool they provide to get the exact drivers you need.
Honestly the rest of the system isn't that horrible. Try to save your pennies while you wait for Diablo 3 and upgrade your graphics card before it comes out. You should be able to get some decent high 5xxx or 6xxx models on the cheap by the time it releases, and those cards with that processor will run D3 smooth as butter.
I would recommend upgrading yourself to an nVidia card instead of ATI though, the nVidia tech works better with Intel.