This is a code only patch - it doesn't update any of the player & club data. It will install over either the original CM 00/01 version on the CD (3.89) or over the previous update (3.89).
The patch is save game compatible - in other words your saved games will be fine and will continue to work with this version. However, the bug that it fixes affected player's attributes, often by dropping them a large amount; if this bug has occured in your existing game then the new patch will not immediately restore the players old attributes (although they may return to their old values over time).
* Player attributes bug
G4 Version Updated
This patch also includes an update for the unsupported G4 only version of the game (found in the Extras folder on the CD). If you want the G4 version to be updated you must copy it off the CM 00/01 cd and put it into your Championship Manager folder before running the updater.