What are the difference b/t xD and sD cards for digital cameras?

Can you use an sD card in an Olympus camera where the storage medium calls for an xD card?

xD cards are about half the size (both physically, and capacity-wise) and cost about twice as much.

It pretty much just depends on the camera/device you get, whatever you have, you're stuck with what they built in to it (so no, you can't use SD for xD).

the x and the s

SD card is more popular than xD and less cheaper than xD. Most likely Olympus use xD for storage

Only Fuji and Olympus cameras use the XD card; besides the Sonys, all other point and shoot cameras made now take the SD card (Nikon, Canon, Casio, Kodak).