You can install DD-WRT on some routers to give them repeater functionality. I have it and works perfectly on my Linksys WRT54GL. I'm not sure if the D-Link DI-254 or AR680W 300N Wireless Router are supported or not, but you can check their website and see:
If the router is supported, just download the firmware, connect to your router that will act as a repeater with an ethernet cable, install the firmware, reboot the router and configure it as a wireless repeater. You enter in the SSID and WEP/WPA key (if you have one) of the access point and create a virtual SSID and security of sorts which will be the second repeater router that you connect to (or you can just plug ethernet cables in).
If your router supports DD-WRT and you get it installed fine, check out this tutorial on setting up the repeater function:
No firmware needs to be installed on the primary router (AP), just make sure the second router is in range of the wireless network.