The XKR is based off the old Jaguar XJS, as is the Aston Martin DB7. Unlike the Aston Martin, the XKR is limited in its top speed to 155 mph. If the computer chip were tampered with to allow better performance, I'm sure this car could reach 170 mph, with some higher performance versions reaching much higher numbers.
There have been several limited edition versions of this car. The XKR Silverstone was a high performance package version of the car with platinum paint and 20 inch wheels. The XKR 100 celebrated Jaguar's 100th anniversay with 500 limited edition convertibles and 500 coupes. They each had Recaro seats, Brembo brakes, and 20 inch alloy wheels. The XKR Portfolio was first made as a US-only product. It is a convertible with Recaro seats and improved brakes. The 2008 version will be available worldwide and will feature the most powerful brakes on any production Jaguar ever. The XKR 4.2S was a trim and performance package limited edition car. The XKR-R is a concept car that will not likely be produced.
The XK will likely replace the XKR tag on upcoming Jaguars.
These cars are available on the used high end car market. You might find these on luxury car dealer lots, or even on eBay.