Using an extra router as an extender? how?

[Chiuy]

Are there any good articles and or even tips from you guys on how to get an extra router working as an extender?
I have a Linksys but the house is too big and can't reach some parts of the house, such as my house which has very weak signal.
I have an extra wifi router that is a D-Link DIR-615. I'm not sure if it can be an extender, but can't hurt to ask.
If it can, how do I make it to an extender? And any other tips on how to increase the wifi signal by like maybe 10 more feet?

(Or repeater, Idk the vocabulary terms for it)

 

[Emerald]

use the DD-WRT firmware and configure it as a repeater bridge (connects wirelessly to router and retransmits signal)

http://www.dd-wrt.com/site/support/router-database

http://www.dd-wrt.com/wiki/index.php/Repeater_Bridge