After you've got PHP5 and Apache running on your Ubuntu development server, the next thing you'll want is Eclipse PDT. Shortly after that you'll need a debugger.
On Ubuntu 8.10, I set up Eclipse 3.4 (Ganymede) with the latest Release Candidate of PDT 2, it took forever because of some slow mirrors, but I'd recommend just buckling down and getting through it. Here's the step-by-step guide I found most useful. If Ubuntu someday gets PDT and Eclipse 3.4 in the repositories then just use that.