What are the difference between the 2 ip addresses? FTP Se..

I have 2 computers sharing a cable connection. I have a Linksys Router and
a Linksys Modem.

When I go into IPCONFIG, it shows my IP Address as 192.168.1.100 but when I
go to a site like "whatismyip.com" it says my IP Address is 69.167.209.xx
where the x's are numbers but I didn't feel like posting my IP address on
the internet.

I set up a FTP Server using IIS on one of my computers and I can access it
from that same PC by typing in ftp:\\192.168.1.100, but if I try and access
by typing in ftp:\\69.167.209.xx., it doesn't work. It gives me an error
saying that "windows cannot access this folder", "make sure you have
permission", "the connection with the server was reset".

192.168.1.100 is your LAN ip address. Judging from the number, I'd
say it was assigned by DHCP. Any computer in your LAN can use this
address, but no one in the Internet world can.

69.167.209.xxx is your WAN ip address and is the address by which the
Internet world knows you -- actually knows your router. Your router
"routes" requests from the Internet to a designated computer. (You
could have hundreds of them in your LAN.) You must tell the router
which computer handles each type of request, if any do at all.

In the case of FTP, port 21 has been reserved for these requests.
Unless you require outside access, I'd recommend that you not open this
port to the outside. Before you do, you should carefully read about
Internet security.

You simply have to find the correct set up screen, usually port
forwarding or UPnP forwarding, and tell the router where to send FTP
packets when they come in. It'll be to one of your LAN machines,
192.168.1.xxx.