Simply remove all LISTEN directives in your Apache configuratian (httpd.conf). The default for Apache is to listen on ALL IPs and ALL Ports.
P.S.: Oops! I just read this note in http://httpd.apache.org/docs/2.1/en/mod ... tml#listen
If it is not in the config file, the server will fail to start. This is a change from previous versions of Apache.
Sorry, I didn't know that the default behaviour has been changed. As it looks, there is no other way than specifying LISTEN directives for each IP, which is assigned to your server (still not very many).
P.P.S.: Maybe I dont understand your question correctly. Apache *cannot* LISTEN to all PCs of your LAN (thats not the way Apache/LISTEN works); Apache can only LISTEN to IPs which are assigned to the server where Apache is installed. All incoming requests to this/these IP(s) are recognized.