I've used XAMPP with PHP on Windows. Easy to setup and use. Supported toggling between PHP4 and PHP5 (I think the default was PHP4). Currently I'm using VMWar

I've used XAMPP with PHP on Windows. Easy to setup and use. Supported toggling between PHP4 and PHP5 (I think the default was PHP4). Currently I'm using VMWare and Ubuntu 7.x (be careful about using Ubuntu 8.x - I've seem to recall that VMWare tools may not have caught up and play well with that version yet). I prefer the VMWare/Ubuntu approach for now since it will more closely mirror my intended deployment on Amazon Web Services (already started playing with an Ubuntu AMI).