Most D-SLR use the viewfinder to compose and take the picture, and you cannot use the LCD to compose your shot like a PS camera.
But there are a limited number of D-SLRs that have live view LCD to let you use the LCD to preview and compose the photo just like how you use a PS camera. These include the Olympus E-330, E410 and E510. I believe Canon's new EOS-1D Mark III has a live view LCD available too. I'm not sure about the anticipated Canon 40D. These may become more popular in the future if there is a demand for it.
However, I do like to use the viewfinder to compose the shots for the D-SLR, especially when I handheld the camera with a hefty lens like the 70-200 mm f/2.8L IS. It will be straining and hard to steady the camera if I use a live view LCD to take shots. You may just have to try it and get used to it. After practicing for a little while, you actually may prefer using the viewfinder. The live view LCD will be nice if you try to take a shot in an awkward angle not possible to use a viewfinder.
I just purchased a canon rebel digital SLR XIi version. I was shocked to find that I can't use LCD screen for image preview. Is tis really true? So the LCD screen is useful only for playback and viewing camera settings?