Collision detection and soft tissue deformation are two major research challenges in real time VR based simulation, especially when haptic feedback is required. We have developed a real time collision detection algorithm for a prototype laparoscopic surgery trainer. However, this algorithm makes no assumptions about its applications and thus can be a generic solution to complicated collision detection problems. For soft tissue modeling, we use the mass-spring model enhanced with volume constraint and, stability control methods. We use both the new collision detection and tissue modeling algorithms in a bimanual hernia repair simulator which performs a mesh prosthesis stapling operation in real time.