I was wondering what is WDS, I decided to give it a try. WDS configuration sounds interesting since the client router will be able to communicate to router A and provide wireless access to laptops at the same time. This would eliminate router C in my previous configuration through "Client Bridge". Although I am aware that the data throughput will be halved behind the "Client Bridge".
I gave up eventually because WDS requires both router A and B to have dd-wrt firmware. This will not be practical for me since my pre-condition is not to alter router A in any manner.
Linksys has a WRE54G Range Expander product that is supposed to do the same thing. I saw its price tag at SGD 160++ in Sim Lim Square the other day. This price is almost equivalent to the sum of 2 WRT54G routers. According to the internet postings, WRE54G also cuts the wireless speed to half. In addition, this device is going to constantly repeat whatever the main router is transmitting even when it is not necessary.
In conclusion, I still think my Client Bridge configuration using 2 routers (router B and router C) is better.