your motherboard has built in sound, so you won't necessarily need a sound card (unless you want uber awesome sound).
i'd suggest getting a Serial ATA harddrive, what size you want depends on what you want to use it for. i'd say about 200GB? they are the cheapest for their size from what i can tell. (note: if you want to install windows XP onto a SATA harddrive then you have to install the drives for it manually because Windows XP doesnt detect them by default. more info on how to do this
here
really what you get depends on what you want to do with it.
/ 
