570uz and external flash

We have been trying to decide between the 570UZ and FZ18. One of the things that leans us toward the 570UZ is the possibility of an external flash. Our current camera (Canon S30) has been disappointing for inside photos requiring a flash (lots of redeye and generally poor color). Will the flash on the 570UZ or FZ18 solve these problems or is an external flash necessary. Also will higher !SO solve some of the problems. We are not talking about really low light situations, just normal indoor photos where there is not enough light to normally take photos without a flash.