When I use default installed php package (php-4.0.3pl1) on
Mandrake 7.2 (default kernel 2.2.17), it lacks socket support, then I downloaded php4.0.4pl1 and compiled a 
self-contained sockets.so module, it works fine!
but since php 4.0.3pl1 has some bugs,therefore, I update to 
4.0.0pl1 as suggested. Then each time I tried to call 
socket() function, it always says "call to undefined function socket()"
I recompile the self-contained module, it still doesn't work
ps.I have enabled extension=sockets.so in php.ini
strangely enough, mysql.so still works fine!