Converting Existing Systems From One Distro To Another?

Sam "Criswell" Hart asks: "I have been using Red Hat on my machines since RH4.2. The reasons were largely due to bandwidth issues and the fact that I could always get the latest RH ISOs for free. However, since 6.2 I have been disappointed with RH, and 7.0 with its not-quite compatible GCC would be very bad for my free-software projects. I have been thinking of switching to Caldera or possibly to Mandrake. However, I am spoiled by the fact that I can just pop in a new RH CD and upgrade my existing system quite painlessly. Because there are so many other RPM-based Linux distros out there, and they have update options, are there any (esp. Mandrake or Caldera) which can relatively easily update systems based on other distros? For example, anyone have any success or troubles trying to upgrade a RH6.2 system with Mandrake 7.2? Is it possible, or is there something significant blocking such a thing?" While updating a system with software intended for another distribution isn't necessarily good idea, are there utilities out there that can perform the necessary operations needed to convert an existing system from one flavor of Linux to another?