Ok to start with, I can only get broadband via gsm 3g so I am using one of these Linksys WRT54G3G routers, like so
_ http://www.expansys.ie/d.aspx?i=129557

Then I have a new type Apple Airport Extreme, the rectangular one. I have installed the linksys router upstairs then ran a Cat 5 cable and plugged it into wan port of the airport extreme, also upstairs which I need for wireless printing/hdd. Everything works fine so far.

Now problems arise, I do most of my surfing downstairs, and the signal is weak, so I want to use my old type Ufo Airport Extreme (have a cat5 between upstairs and downstairs) to boost the signal, and so far I am having limited sucess setting it up reliably.

My question is whats the best way of setting up my gear, which is really three wireless routers.
Which should allocate the ip adresses, which is wds main/remote or relay, manual ips or dhcp etc.I have tried lots of permutations in the airport menus and got it all working at times, then the ips go haywire or I lose internet connection etc.
Any advice ?? and be gentle, because as you can see, I'm not an expert in macs or networking, or anything else either.