In a LAN with both DHCP and statically assigned IP addresses, to determine, using Ping, what IP Addresses are in use, ping xxx.xxx.xxx.255 where xxx represents the network id e.g. 192.168.0.255. Then arp -a to list live ip addresses on your subnet. Compare to dhcp scope and you have your list of static ip addresses in use.
Using Ping to determine what IP Addresses are in use in the LAN.