Which software for packet sniffing and wireless signal stren

[eugeneg]

I would like to install software to help me identify whether any machine is using an IP addres already allocated elsewhere. Perhaps a packet sniffer that could list IPs and corresponding MAC addresses would be ideal. Would someone please suggest such a package.

I also have wireless signal strength problems and would like to run Inssider or something similar. Any suggestions welcomed.
I tried to install Inssider but failed. See
http://www.metageek.net/forums/showthread.php?7234-How-to-install-for-absolute-beginners&p=21948#post21948

thanks.