We have an airport extreme, airport express and a Sony PS3. Are we able to use either to stream iTunes/iPhoto to our Sony PS3?
In this case the PS3 is a DLNA player, not an AirPlay device. Two different technologies for streaming. You would need a DLNA server to stream to the PS3 as iTunes itself does not provide this type of service. There are a number of options out there. One example would be TVMOBILI.
also, are we able to use airport with WD MYBook Studio (2TB) as a network storage device? If so, what steps do we have to take...?
No with the AirPort Express; yes for the AirPort Extreme. Basically you would connect the HDD to the USB port of the Extreme, and then, use the AirPort Utility to configure it to be shared out on the network.
Using AirPort Utility v6.x: AirPort Utility > Select the Extreme > Edit > Disks tab > Enable file sharing