Allow me to recommend that you check prices before you buy. Amazon has the 400d for $674.00 and the 30d for $1,121.00. B&H will most likely have the same prices. That is not a huge difference from what you quoted but that is money to go for better lenses.
Most folks agree that you should go into a local store and feel the camera. Finger it a bit. See what you like. I think the reviews will support that the 30d is somewhat better hence the price difference.
That is a tough one...the 400D is a lower level body but has newer technology. The biggest difference (besides price) is the ergonomics and user interface. For many people, the 400D (and the Rebel series) are just too small and hard to control. Personally, I bypassed the 350D for the 20D because the feel and layout of the 20D was a much better fit for me.
I suggest you go to a store where you can feel both cameras. It may become clear which one feels best to you.
Still, the price difference is rather large and difference in the image quality is most likely negligible. I say that if you used the price difference to buy a better quality lens...then the image quality would be better than the 30D with the cheap lens.
I was faced with the same decision. Even though the 400D is newer, I like the 30D more. It just felt better in my hands. So I decided that I would save the money until I could afford the 30D. (I'm slowly getting there.)