For the second WRT54, you really, really, really, want a WRT54GL model. That's the only one that you can safely assume will do everything.

In this case, the ideal setup would be to configure both routers for something called WDS, assuming your existing unit has that capability(?).

But failing that, the new WRT54GL you acquire can be upgraded to DD-WRT firmware, and then set up as a universal repeater. In that mode, it will do the job nicely, with zero changes required to the existing setup.

By the way.. ignore everything you read anywhere about how to install DD-WRT. The standard instructions are hopelessly complicated for some oddball reason.

Do this instead: install Tomato firmware from the web GUI's Upgrade Firmware screen. Reboot the router and it will come up in Tomato mode. Normally, this is good enough, but Tomato doesn't have universal repeater functionality. So now, use the Web GUI again to install DD-WRT in a single-step.

Trust me, this is way simpler and more fool-proof than the recommended installation for DD-WRT.

If you choose to go this kind of route, then post some more, and we (collectively) will talk you through the nitty-gritty.

Or I could pre-configure a WRT54GL to "just work" and mail it to you. Seriously. I have a few on the shelf here that I got for $35+$5ship+tax each.

Cheers