If you want to use PHP5 + eaccelerator, make sure you following the follwing:
1) Instal eAccelerator CVS version. Most of the bug fixes are for php5 and the releases are too slow. So get CVS and install every 2 weeks or when something changes in the tree.
2) Disable code optimization within eacc. Just enable the caching part.
3) If you need optimization, install Zend Optimizer as it works well with or without eacc.