make WRT54GS into wireless repeater

Hi all, have to admit that I'm a bit of a novice and still confused between routers and access points. I have a Linksys WAG325N Annex 1 that I use as my main ADSL connection. I connect wirelessly to that with various devices.

I have a spare WRT54GS that I would like to connect wirelessly to the WAG325N and then connect a Yamaha keyboard to via ethernet cable (and possibly use it as a wireless range extender if its location lends itself to).

I'm guessing I want to set it up as a wireless repeater, or am I changing it to an Access Point. To change it to a AP didn't seem to come up as an option on the web based setup page for it, (is this because it is only a router and not an access point?).

If I can do it, do I set the SSID's as the same?

Do I use the same channel?

Because I use the wide-40MHz radio frequency on the N-technology WAG325GS, is this a problem for the G-technology WRT54GS?

What are the other settings I'd need to change in the WRT54GS, do I need to change MAC address etc?

Thank you, I did search and found a similar question for a WRT54G but it seemed to be slightly different.