In interventional radiology, inserting a needle to perform a biopsy requires a high haptic sensitivity. The traditional learning methods based on observation of skilled clinicians and training on real patients are questionable. Virtual Reality (VR) surgical simulators have previously been shown to be efficient for training. However, there is a lack of guidelines to ensure the fidelity of these simulators. In this paper, an iterative design approach is used to design and evaluate the user interface for a VR needle insertion trainer. Two experimental studies were conducted to evaluate some aspects of the system user interface. Results permit to validate some design choices and suggest future design directions to improve the interface and environment fidelity of the system.