You need to google search for 'GTA SA RADAR MOD'.
Extract the download to a new folder.
You need a tool name Spark, google 'GTA SA IMG SPARK'. (Dev and Snoopy use an alternate IMG editor, but I can't remember the name)
Open 'gta.img' and import the files from your new folder. (This file is located in your main GTA SA folder, inside a folder named 'MODELS')
Then click 'SAVE'.
You also need a tool name IMG-TOOL, again google it.
Open the 'gta.img' again, then click 'REBUILD ARCHIVE'.