Hi,
Although the WHS overheads mean that it isn't the speediest server in the world, restricting it even further by using SATA 1 really would be a retrograde step.
Also, as this is a server, the first thing to do, is confirm that you can get Server 2003 drivers for the SATA and NIC etc.
Doesn't matter about sound, it won't be used, 2DVD drives are overkill, will only be used to install the software and then may never be used again, same goes for the video.
If you can get Server 2003 drivers, you could always buy a PCI SATA card, they are cheap enough nowadays.
Colin