Just to add on. It seems to me budget is your main concern?
If you don't mind the size of a DSLR and you are sure you will use it then get the Pentax K-X.
You really have to consider the usage. There are times when I go out meet friends and just don't feel like carry the DSLR. A DSLR has lots of things to learn and take note of. IF you don't think you are that into photography I would say a PnS will do more good.
If you have shortlisted these based on price, please do take into account that the the DSLR will work out a bit more than the listed price because of the accessories that you always end up buying.
Among the other two, I personally have the P100 but I believe the Canon is a better camera.