Asus showed had a P35 board with a 64-bit PCI-X slot on its stand and this board is specifically meant for entry level workstations. The P5K WS is otherwise not that different from most other P35 boards.
It's got a single x16 PCIe slot, two x1 PCIe slots and two standard PCI slots in addition to the PCI-X slot. The PCI-X slot has its own controller chip which is located behind the two x1 PCIe slots.
Asus has also fitted IEEE-1394a or FireWire 800 to this board and it's got dual eSATA connectors.
It has a rather small heatpipe cooling solution for the chipset compared to most of Asus other boards that are on its stand this year, but more on this later.
This is what the board looks like: