Elements, being the less expensive ($75, retail) consumer version of Photoshop, has a heavily de-featured version of Adobe Camera Raw (ACR), Adobe's Raw converter.
CS5 ($699, retail) is the current version of Photoshop and includes ACR 6, unless you opt for CS5 Extended ($999, retail) for the 3D and scientific editing features. CS3 uses ACR 4, which hasn't been supported for several years now.
Photoshop Lightroom 3's editing function also uses ACR 6. The interface looks a little diffect from Camera Raw in CS5 but they are essentially identical. Of course with Lightoom 3 ($299, retail) you don't get msot of Photshops best editing tools like layers, and the precise selection and masking tools Cs5 has. Lightroom is primarily image database management software, the editing function is secondary. Adobe designed Lightroom to be a compliment to Photoshop, not a replacement for Photoshop.