The biggest change from PHP4 to 5 is the object model. Most code is backwards compatible. If your code uses a lot of OOP you may need to take some time to rework that code. Otherwise there's not a whole lot of difference... if you're having difficulty with a specific chunk of code you should post it.
I don't believe any announcement has been made. I have heard that they will be adding namespaces though.. I'm sure that will make C++ programmers happy.