Transparent mode on a 525

Trying get the transparent mode figured out. I have the 2950 that I pluged into int e0 interface of the firewall and then the took int e1 and pluged that into a 3750. The ip subnet that the firewall is plugged into is 192.168.86.- range. What should the ip addressed of the firewall be. Dont want to use private address. Just want to use this firewall in transparent mode. Also I anybody might have a basic config that is working in transparent mode that they could paste on here. Thanks