php4.x won't work under apache 1.3.x

I have installed apache and php on my laptop, and there was no problem. 
tried the same thing on my desktop today, but couldn't get it working!

in the apache error log, basically it says it couldn't spawn child process 
for my *.php files. and also ask me to put "#!" in the first line of all my 
script files.

i dont know if this is a more apache related question or php related? so i 
kinda asking help from both end.

-larry