This limitation may not upset desktop users too much; 64-bit desktop processors have been around for a while and include all AMD Athlon 64 and Athlon 64 X2 chips as well as all Intel Pentium 4 6xx, Pentium 4 5x1, Pentium D, and Core 2 Duo chips. However, Microsoft's decision will likely miff users of HD DVD- or Blu-ray-enabled notebooks like Sony's Vaio AR190G, which includes a 32-bit Intel Core Duo processor.
Update: The situation is apparently a little more complex than first reported. A U.S. Microsoft representative has told CNet that 32-bit versions of Windows Vista will be able to play back Blu-ray and HD DVD movies, but that they will require third-party software to do so. The rep says it's up to software vendors to decide whether to support 32-bit systems. Since, according to the first story, Microsoft's decision to limit built-in support was due to requests from media companies, third-party software vendors could face similar pressure to leave users of 32-bit systems behind.