I downloaded maps from planetquake3.net but none of my maps I put into the map folder worked. I Went as far as removed all the ones I added and only put one in but it still didn't work. Then I updated it with 1.32 quake point.
Step 1: Download the new map you want.
Step 2: If it is a .zip file, unzip it and place the .pk3 file into c:\program files\quake iii arena\baseq3\
Step 3: Load the game. Load the map via the menu system or alternatively type \map themapname at the console.