Hi Adel
plase use google to inform about the two possibilities and the pros and cons about
apache with mpm-worker + libapache_fastcgi & suexec for php
vs
apache with mpm-prefork and mod_php
The default installation for ispcp is using fastcgi and mpm-worker.
If you follow exactly the steps in the install guide, you will get this.
If you forget to change the sources.list for aptitude then libapache_fastcgi will not be found. But you can download it separately:
http://packages.debian.org/etch/libapache2-mod-fastcgi
uninstall mpm-prefork and mod-php(4 & 5)
/J