For somebody just getting their feet wet where should i begin? php4 or php5? Is it better to start with php4 or php5? Im coming from a c++ background

just start with php5 as it is an 'ímprovement' on php4 and thus CAN have some diffrent new syntax options. For the rest it's the same.
I once started with php3 and when i tried php5 it was still able to do what i did a while ago (it still has most of the options and functions from the older php's) but i am now also able to do a whole load of new stuff.