I'm trying to make sense of the inquiry that you had posted...
First of all this is a pentax dslr forum. I really can't comment on the canon
s3 is, 350D, nor the 300D. Second, which I think is the main question you are contemplating is whether or not you should upgrade to a dslr or not. The big
factor when considering upgrading to a dslr is costs. Making the leap from a prosumer point and shoot to a dslr is quite a bit of money. You really have to
consider how serious your commitment to photography is going to be since later
on there will be additional costs as you acquire additional lenses. If you are looking
for an entry level dslr, the cheapest pentax would be the *ist DL with the 18-55 kit lens. The 18-55 kit lens is actually quite good and would make for a great lens to start with.