have you deleted all your networks in the pref pane then hit apply. after that then add the Ethernet apply then WiFi and apply, set the service order after installing both back.
d620 bios should be modifiable with phoenix bios editor. you need a fresh bios installer from dell plus an rw report and compile on the same machine. if it's dsdt that you want to edit then you need to have it pause at dsdt while compiling so you can edit the dsdt.
yes that simple..... you can even partition the drive if it is GUID formatted from with in diskutility then make a clone on the same active drive. it will show in chameleon as another install.
i highly doubt any of those software's will backup chameleon... but you should be able to reinstall chameleon. as for time machine.... im sure it would be a very slow process if at all possible. you can also just partition a disk and clone your install.
you can try with this experimental kext found here http://www.insanelymac.com/forum/topic/247470-bcm5722-bcm5754m-bcm5755m-bcm5787m-and-bcm5906m-nic-driver-3264-bit/