Here are the complete set of instructions:1)Put the .pk3 file into the /baseq3/ directory inside quake 3. OR if it's a .bsp file, place it in /baseq3/maps/ folder (make if necessary).
2)Load up Quake 3
3)Type into the console (hit ~ to bring it down):
/sv_pure 0
4)Type into the console:
/map mapname
for instance: /map mymap
will try loading up mymap.bsp from /baseq3/maps/
Good luck.
If you don't know the mapname, rename the .pk3 file into a .zip file and look at the name of the .bsp file.
--------------------
Talk is cheap, so is my signature.