Virtual Reality Exposure Therapy (VRET) has been put forward as a treatment for patient suffering from anxiety disorder such as social phobia. Current VRET systems however provide limited speech interaction possibilities between the patient and virtual characters and therefore does not seems to offer patients an exposure to the full richness of an actual human-human dialogue. One way to support a free speech dialogue between a patient and a virtual character is to develop interactive pre-scripted dialogue scripts and where specific patient answers can trigger pre-recorded avatar responses thereby creating extensive dialogue trees. This paper discusses this approach and a dialogue editor to write these dialogue scripts. Online chat bots are proposed as a technique to evaluate and to improve an interactive dialogue script. Results of a pilot study with 4 non-phobic individuals are promising and suggest that these scripted interactive dialogues can be used to simulate a human-human dialogue.