Apple AirPort Question

I just got an "AirPort Express Base Station" and I want to use it as a repeater for my wifi network.

My main router in the middle level creates the wifi network for that level and upstairs, but in the basement is where the wifi signal is weak.

I found this link that seems to be what I want, but I don't know what it takes.

My main router is a Belkin N1 and it connects to a D-Link DGS-2208 hub that connects to several outlets in the basement. It is here that I connect my AirPort.
I also have an old linksys router in the basement that I have been using before I got the AirPort.

Would it be possible at all to use the AirPort as a extender?
If someone could help me with this I would love it!

Thanks.

 

It looks like my Belkin router(F5D8231-4) does not support DD-WRT, so the option is Not available.

 

My old linksys(WRK54G) does not support DD-WRT as well, looks like I have bad luck


Knowing all this, what is the best way for me to utilize my AirPort Base Station?