For everybody who is frustrated by the not working of 'pear install ps' command under most likely SuSE, at www.hipersonik.com/php_ps_pslib.html is a possible way to get it working. It is also possible to use these instructions under other distributions.
If 'pear install ps' works fine from the start (pslib etc is installed), but ps does not work yet, use dl('ps.so'); This will save you a lot of time.