Pretty self-explanatory. Looks like an okay dual-antenna wireless-N router with 4 10/100 ethernet ports. Note that it is not a modem.
D-Link product page: http://www.dlink.com.au/products/?pid=565
Seems to be in-stock online and in most stores.
Cheaper than all shopbot listings: http://www.shopbot.com.au/pp-d-link-dir-615-price-80279.html
No it's got nothing to do with the router per se.
You download two firmwares - one from DLink and one from DD-WRT. Just need to make sure the DD-WRT firmware has the same ID as the DLink version - by comparing the last lines of each in a hex editor.