Maximum PC

Okay I feel like a 'tard asking this but what is meant when something says, "Must be within the same IP 'range' as your current network".

If I set my routers start address to 192.168.15. 100 and number of address to 50 is my range 192.168.15.100-192.168.15.149?

I'm trying to connect a wireless router to a wired router network. The wired router's IP is 192.162.15.1 (this is the address I use when logging via a web browser).
This router's Start Address is 100 with a range of 50. So anything plugged into the router is 192.168.15.100 or above (up to 149).

So far so good???

Okay now I'm plugging in my wireless router (Linksys WRT54G) into one of the wired router ports so I can use my iPhone and laptop in other areas of the room but I"m having a hard time with the setup.

I've read from others that the downstream router (in my case the wireless one) needs to have Auto DHCP disabled and the IP set to Static.
I've tried to set the wireless static IP to something within the .100 range but keep getting an error saying the WAN and LAN addresses are the same.
As for wiring I'm using port 2 of the wired router and plugged into port 1 of the wireless router (NOT the Internet/WAN port).

Can someone look at the screenshot below and tell me what settings I need to enter?

You need to disable DHCP server on the wireless router, you can let it receive an IP by DHCP, you just don't want it to serve IP addresses.