How can I get
help for PHP 4.3.10?
You could try one of PHP's mailing lists.
What are the differences between 5.0.x and 4.3.x?
Read the PHP Manual to find out.
The main differences are in OOP support, additional functions (especially DOM, SimpleXML and SPL), and that MySQL is no longer default (replaced by SQLite), though still available.
Do the scripts that worked with php 4.3.4 will work with php 5.0.x?
Most of the time, yes.
If you can tolerate the known bugs in PHP 4.3.9, and PHP 4.3.9 compiles and works for you, then use PHP 4.3.9
If not, then you can either risk PHP 5.0.3, or wait for PHP 4.3.11