Buying a Canon EOS 450D ?

The first thing that I am wondering is why you are looking at the 450D. What is it that you are looking to get out of it? Answering that will give you a better idea of what the cost will be. The S5 is a wonderful camera, in the dslr-like category, that gives you a lot of the perks of a DSLR, without the huge price. Of course there are somethings you can only get on a dslr.

Right now the 450D body only is around $800 (the body with the kit, all purpose lens, is a bit more but prices are dropping). The kit lense will give you the range for "standard" pictures, but you will need to change lenses to zoom. A good zoom lens to give you the distance that you want will be $400 - $500. The S5 already has a zoom up equivalent to 432mm, so to get any improvement you would need to get a zoom lens with something like 70mm - 300 mm (which on a canon would be equivalent to 112mm - 480mm). Bigger lens exist, but the price just keeps going up.

You will notice a great improvement in picture quality though. The 450D will just take nicer, sharper pictures...no questions about it. It has a bigger "brain" and will better be able to figure out what would make the pictures look better. Plus you will have more control to make the picture do what you want. I think before you start investing too much money in on it, you might want to do some more research online or pick up a book on basic dslr functions. It can get really confusing in the beginning until you understand what the terms all mean. There aren't any stupid questions when you are actively trying to learn something new.