Yes, the answer is to change the IP address of your router, and here's why?
Unlike a cable modem, a DSL modem is a gateway, a pseudo-router in its own right. It has its own IP address and configuration page if you were to type that number into the address bar of a browser. It also typically has a DHCP server so I can assign an IP address to your computer.
The problem with hooking up a router in-line with your DSL connection is that typically a router is also a DHCP server, and its IP address is usually in the exact same subnet as the DSL modem. In my case, the router was at its default 192.168.1.1 and the DSL modem was at 192.168.1.254. Well the DSL modem's address happened to be in the range of assignable addresses for my router, and vice-versa. So basically the situation was two DHCP servers fighting over the same range of addresses. I changed the router's IP address to 10.0.0.1 and all was well, but pretty much any address that wasn't 192.168.1.x would have worked. By putting the router on a different subnet, you basically separate two fighting territorial wolves and give them each their own space to control.
A word to the wise, DO NOT call your DSL technical support. They are not equipped to handle wireless router questions.
Of course the simplest solution is the buy a DSL modem with a built-in wireless gateway in the first place.