The enhancements of PS2 on old games are texture interpolation (like BI-filtering) and faster CD loading times. One of the best examples of both is Tekken 3.
Some games are incompatible with the enhancements (Silent hill can’t use either and Metal gear can’t use the CD speed up without bad glitches.)
(Remember, you have to re-enter the PSOne driver menu each time to re-do the settings)
From the main menu, press Triangle to bring up the Version info screen. This screen shows the version numbers for the various functions within the system. Select "PlayStation® Driver" and press the Triangle to bring up the driver options.
Drive Speed sets how fast the drive reads the CDROM. Fast is the upgrade, while Compatible is normal speed. Some games (such as Final Fantasy VII and VIII) experience glitches when running under the Fast option as they were programmed with carefully calculated disc access.While it doesnt make a massive difference (the load times on games that work with this are only decreased by about two or three seconds), it is a very nice option.
Texture Mapping smooths out textures in the games that it is used on. Again, not all games will work with this since some used software tricks to enhance the textures in the game when running on the existing PlayStation.
Note: if you do encounter a problem with a PlayStation game while running one or both of the enhancements, simply turn it off from the menu