Thanks for your reply
I have a "starter" Canon kit, because I didn't had money to buy a better kit
I already was a wedding photographer on some weddings, not on many though
Now, I already sold my kit and want to buy a new one, and as I will make also wedding photography I have to choose one with "fast" autofocus to catch the moment.
Originally I wanted to buy the D90 kit + flash, but after that I saw the Pentax DSLRs with a wealth of functions.
Then I wanted Pentax, but after that I read a thread on a forum, that the Pentax cameras has a difficulty autofocusing in low light.
Now I really don't know which to choose.
)
Also, I can borrow some money from my brother and I could buy also the 50D + 17-85 + flash.