430 EZ speedlite

Is it possible to use the 430 EZ speedlite with a conon 50D

Yes, but only in manual mode.

I would recommend using the camera in Manual mode, ISO400, Aperture F/5.6 or f8.0, Shutter Speed about 1/125 and the flash in Manual mode set to 1/2 power and tilt the flash head up to bounce off the ceiling.

Then adjust the power after each shot to get the right exposure.

Bouncing off the ceiling should give you more consistent results. With straight ahead flash the exposure will change each time the flash to subject distance changes. With bounce flash the ceiling is the main light source and the exposure will not be so critical.

On camera the flash is great in Manual mode(it can work in TTL on 1d series cameras)
Off camera it has a really annoying power saving feature that shuts it down after a few mins
If you pick up some ETTL triggers like the pixel knights i believe these will "wake" the flash up on half press(the flash wont work in TTL mode .. i believe)

Tom