Somewhere down the line you are going to have to wip the side off, and take a look inside, so sooner rather than later! this way you will see if you have any available PCI slots and a dedicated AGP slot for the graphics card.
It is almost certain that you will have at least one spare PCI slot, this you can use for your new sound card.
If you are lucky enough to have an AGP slot (maybe your present card is AGP?) then use this for your graphics upgrade (this connection is superior to PCI and AGP cards are cheaper and more redily available)
You may not have the dedicated AGP slot on your board, in which case you will be after purchasing a PCI version if you have enough PCI slots that is.
Martin Vote if you found this post helpful please!!