Hi, i would say the 400d can definately achive this kind of shot yes. Afterall, i used a 350d and the 400d is an upgrade to my camera
with regards to the equiptment you need to invest in the world is your oyster so to speak. its all dependant on budget. i used my canon 100-400L series lens @ the 400mm end, which given the crop factor of the sensor works out to be 640mm. now remembering that this is at least a 100% crop of the original image i could have done with a much longer lens
i found towards the end of the eclipse due to my lens being F5.6 at the long end it wasnt registering the slight redness in the moon which i got where i live, i think an F2.8 lens may have captured this but i cant be sure. also its definately worth getting a sturdy tripod for this type of shot and also a cable shutter release which is how i took my shot, as it would be near impossible to do handheld.
hope this helps, if you want/need to know anything else please ask
thanks
Antc