really need to know a bit more to advise on the Graphics card.
There are three different sockets used at the moment for graphics cards
PCI (old and slow) - PCI is still used by computer but it is generally obselete at the moment.
AGP - (most common) AGP is still in a lot of machines currently about
PCI-E (newest and fastest) PCI-Express is the latest socket and fastly bnecoming the norm, any new computers will generally be PCI-E
I would guess that the PC your getting will be AGP, knowing the cpu and motherboard will enable us to get a better idea of whats the best option with regards to upgrading the graphics.
On board sound will usually do the job perfectly fine but dont expect any mind blowing cinema sounds coming out. A soundblaster Audigy 2 (or 2ZS) is not very expensive at the moment and an excellent upgrade for decent sound