While DirectX was primarily designed for Windows 95/98 and the newer Windows 2000/ME operating systems, the latest releases starting with DirectX 6.0 Media also offer support for Windows NT 4 (with SP3). These DirectX drivers will work with any game that has been written to take advantage of DirectX. For more information on DirectX, check out The Adrenaline Vault's DirectX FAQ or Microsoft's own DirectX Web Site.
Pros: A must-have for games that have been written for DirectX; MMX support
Cons: Not all games make use of DirectX, no Win 3.x support, partial support for NT 4