If they Lower Control Arm is staying on the Car; People have said that you can support the Lower Control Arm on a something like a Jack Stand and let the weight of the Car keep the Spring Compressed while you remove the Spindle/Steering Knuckle from the Lower Control Arm so that you can change the Ball Joint the as Don said is actually in the Spindle.
If the Lower Control Arm is coming off you need to compress the Front Spring.
I have tried to use the Strut type Coil Spring Compressors 2 times. The First time I bent them. I replaced the Threaded Rod with thicker 5/8" Threaded Rod and they also bent.
(If you use the $189 copy of the Klann Coil Spring Compressor you may need to enlarge the Hole at the top ot the Spring Pearch.)
After that I made my own Spring Compressor that compressed the Spring up into the Spring Pearch. First Pic.
Another Member made is own Compressor:
http://www.peachparts.com/shopforum/showthread.php?p=987680
The last pic shows the right type Spring Compressor in action.