The modswitcher3.rar file you have requested: GTA IV / Tools / Modswitcher V3 - 2.18mb is not available. Perhaps try browsing all files for the game Grand Theft Auto: San Andreas and upload any files you want to share or are missing. This is the only information we could locate:
Here is a program that will allow you to switch between your modifcations in GTA IV, this will also work with all versions of GTA 4 (from the first version to the latest patch). Although it should be mentioned that the readme is in German.