Using second router to boost wireless signal - total newbie

Hey there, I have trawled tons of threads on this precise same topic (so forgive me for the repeat), but am still drawing a blank. My tec know-how seems to be too weak to understand a lot of the responses, so hope you can give me some ABC help.

Situation: Router - an EchoLife HG520c - is downstairs. Poor wireless signal upstairs, need to boost it. Have an old Westell 327W router that I want to use to do this. But I want to connect them wirelessly (a cable connection would be a construction nightmare in this house.). So how exactly do I do it?

Some details: The Westell 327W is not DD-WRT compatible as far as I can see and so it seems that it has to be my primary router. But the Echolife has a bridge mode (under WAN settings in the configuration page). Being a tec pleb, I was hoping I could just set the Echolife to bridge and then everything would fall into place, but no such luck. The Westell continued to work fine but I got local connection only with the EchoLife. What else do I need to do? I tried disabling DHCP on one and on both routers but that had no effect. Do I also need to temporarily connect the two routers via Ethernet or something? If so, to do what?
An additional detail is that the computer connected to the Westell is Windows XP, but the two laptops downstairs are Windows Vista and Mac. Mac network preferences seem to offer a lot less options than on Windows.

Would really appreciate your help with this. Thanks!