The R-Style is a performance enhancement that can be applied to both the XJ and XK Jaguar models. The R-Style Jaguars include a supercharger placed atop the already-powerful V-8 engine, and retuned steering and suspension.
The XKR models will appear later on in 2007.  The entire XK series has been redesigned this year, but not past the point of recognition.  Many of the previous styling cues are apparent, but the new XK gets a longer wheelbase and all-aluminum construction.  
The XK series includes luxury and convenience features like leather/power/heated seats, walnut or poplar wood trim, DVD navigation, a premium Alpine sound system, Bluetooth, keyless start, full power accessories and parking sensors.  The XKR is differentiated from the XK by a mesh grille, special badging, 19 inch wheels, quadruple exhaust, and adaptive headlights.
Other performance-minded upgrades can be found throughout the XKR.  The supercharged 4.2 liter, brings the horsepower count from 300 to 420, and torque jumps from 310 and 418 pound-feet.  A sportier version of the adaptive suspension and a more responsive steering system are also included.