In reply to Eann:
The XXXXD cameras are lower models than the XXXD - so although the 1100D is newer than the 450D, it's lower in the range so has less features in some ways, but better features in other ways.
If you just want a general easy DSLR that you are never going to go into manual mode for, then the 1100D has a slightly better sensor and limited movie ability.
Otherwise, the 450D, as a model further up the range (albeit it older), has some more semi-pro features, and it's an excellent camera to being learning how to use a DSLR. It was my first DSLR, and I still use it as a backup camera or when I don't want to take the 7D out and about.
In terms of image quality, they are generally going to be fairly comparable, with a slightly better higher ISO performance on the 1100D.
