You need to be very careful about using terms like HD since, as posted above, HD can mean a very low (In terms of photography) resolution that may even be worse than your current camera.
Although, don't be fooled by megapixels - they don't ensure you'll get a better picture.
Quick example:
http://www.amazon.co.uk/exec/obidos/...A3P5ROKL5A1OLE
Costs £2939 (not even including a lens) and has 10.1 MP
http://www.tigerdirect.ca/applicatio...600&CatId=3625
Costs $280 and has 12MP
I'd be very confident in saying that with even a crap lens on that 1D you'd get a much better photograph that with that second camera even if you left both camera on full auto.
If you give us a price range then we may be able to help you out a little bit more.