The right distro is Kamikaze, checkout last trunk and select AR7 as cpu (AR7 target is only in trunk avilable). Try then following instructions on http://wiki.openwrt.org/OpenWrtDocs/Har … /DSL-G604T (my DSL-G664T has cpu TNETD7300, so chances are good on this side)
First of all you should familiarize with bootloaders, serial consoles, etc :-) No, seriously, you could brick your router!
Find out what kind of bootloader your router uses. Telnet to 192.168.1.1 , if you get a prompt try 'ifconfig' or 'nvram show' to find out what is the bottloader's address (mine is 5.8.8.8, ADAM2 bootloader). Then follow istructions on the wiki.
If you're an hardware geek, find out if and where the pins of serial console are. Getting it to work is a great help, as you see the whole booting process even thou kernel then panics. Probably you need a TTL-RS232 adapter, as such routers have 3.3V serial lines. And yes, hi res pics are welcome, please post :-)
Sure it is possible to flash original firmware back, but i have no idea how; so you're warned!! If you decide anyway to give it a try, please report results then.
Buon divertimento :-)
Andrea