An IP address can be set on a computer! Its called a static IP address. The IP address can also be provided by a DHCP server, an adsl router can act as a DHCP server, so the IP address from the ISP may not be the same as the computers IP address.
If your considered to have Dynamic IP address then your IP address can change, it is wrong to state that it dosen't.
Also asking someone to switch off all their security when trying to connect to the internet, is not good advice.
but then you probably know all this!