I've been playing with a Netgear DGN2000, which is a very close relative of the DG834GT et al. However, the image tagger supplied with the GPL sources fails to generate correct image files and hence it is impossible to create custom firmware for it.

I've done a bit of reverse engineering and created a version of imagetag.c specifically for it if anyone is interested. I'm not sure if it is useful for the OpenWRT developers or not... if it is then please let me know and I'll e-mail it/post it/whatever.