For a safer and more convenient operation, a car navigation and assistance system with speech-enabled functions is essential. This chapter addresses two challenges for this purpose. The first is that the speech signal is inevitably corrupted by the ambient noise coming from the car. The distance between a hands-free car microphone and the speaker makes this problem even more serious. In this chapter, an integration of a perceptual filterbank and subspacebased speech enhancement are presented to reduce the effects of the first problem. The next challenge is that traditional spoken dialogue systems (SDS) merely concentrate on the interaction between the system and a single speaker. For this reason we are motivated to conduct a further study on multi-speaker dialogue systems. Here, the interactions between multiple speakers and the system are classified into three types: independent, cooperative, and conflicting interactions. An algorithm for the multi-speaker dialogue management is proposed to determine the interaction type, and to keep the interaction running smoothly.