Ping return for down hosts

[Thomas Gaume <tom flwireless net>]

I have a problem, I need to find a script/program that will take a block
of IP addresses and answer ICMP ping request for those addresses if the
hosts is not available.  The reason for this is we are an ISP and must
show consistant 80% usage of our assigned IP addresses at any time.
This program should just basically capture the ping request and check if
the host is answering, if not then answer for it.

I am not a programmer so writing this could eat up alot of my time and I
basically have no idea where to start.