I believe their are CM7 builds for the D2G but their not official ones...I think the D2G will be officially supported for CM9 tho
prolly not for another month or so til nighlies I would imagine and its impossible...Motorola locked that shiz down like fort knox...noone can break in :/
You only need root to flash custom ROMs...you need an unlocked bootloader to flash kernels and such but you can only do that on the OG Droid and Nexus because those are pure Google phones and arent locked down.