Well, it's a celeron D processor, and it is unknown if the motherboard that comes with that system will support a faster chip, The Celerons are not what you would call a gaming CPU. So that would need to be upgraded.
The Intel GMA950 onboard video card is crap, but you can upgrade with a new card, so that's ok. And it only has 512 of ram, Vista needs at the minimum 2 gigs to run at it's best.
So for $199, you will be getting a case, keyboard, mouse and a harddrive.
Not worth upgrading at all! You would be much better off just starting from scratch and building your own.
That system would be ok for surfing the web, email and that's about it