To answer your questions, in their order:
which SSD would be compatable with the Intel dx58s0 motherboard.and a i7980x(6 core)extreme processor
which graphic card to use
Whatever fits your budget, and is PCI-E 16x compatible, which would be most of them.
which sound card to use
Don't need one, onboard audio is fine.
which are compatable.
whether to use three dddr3 memory cards or one.
On the Intel mother board you mention, you can use one, two, or three cards, but oddly that 'board does not support triple channel mode (three cards.)