In GTA San Andreas, the easiest way to install mods is with the help of SAMI. You can download SAMI from the ModDB website. The SAMI application is just a simple program that automates and makes installation easier for the TXD files.
Download ModDB: http://www.moddb.com/downloads/sami-v11
Download and run the program, then select the TXD file and confirm the installation. Restart the game and you should have the items available for playing.