The Effect API has been modified in XNA 4.0. Effect parameters work as usual, however the following:

effect.Begin();

foreach(EffectPass pass in effect.CurrentTechnique.Passes) {
	pass.Begin();

	// Draw

	pass.End();
}

effect.End();

Is now

foreach (EffectPass pass in effect.CurrentTechnique.Passes)
{
    pass.Apply();

    // Draw
}

Or, if you are using a single pass technique

effect.CurrentTechnique.Passes[0].Apply();

// Draw