The "powerful 3D rendering and animation environment" that comes with the Windows XP Plus! pack isn't entirely compatible with several major graphics chipsets, according to the relevant system requirements page. ATI Radeon and Rage 128, Nvidia RIVA TNT2 and GeForce won't run some (unspecified) Plus! features, while 3DFX Voodoo, Savage 4 and Savage 2000 have "major compatibility issues" and aren't supported at all.
This won't be a huge surprise for 3DFX users - Microsoft's hardware compatibility list shows only that most Voodoo cards pass "basic compatibility requirements for XP - but it's a bit of a bummer for manufacturers who've shelled out the cash and shipped Microsoft the gear for Windows Logo Program 2.0 certification.
This programme is intended to provide compatibility guarantees for hardware running with Microsoft operating systems; a big pile of lists of what's passed at what level is available here, and ATI has this certification for Radeon on XP. According to the list ATI has also been a consistent goodie two-shoes in getting certification for Win2k, certainly compared to many of the other manufacturers. ATI's Radeon 7500 is currently shipping as "XP-ready."
But even if you're certified for XP, Plus! for XP isn't necessarily covered. According to the Windows Logo Program overview, anything submitted for testing must: "Maintain system integrity. The implementation of the technology must not adversely affect the performance or stability of all functionality provided under the preinstalled operating system and under Windows XP/Windows 2000."
News source: The Register