Most modern Linux distributions have a method of updating the system without requiring a clean install. The exact procedure for this varies by distro.
Yes. BackTrack is a Linux distribution that focuses on penetration testing and computer forensics.
Yes.
No, Ubuntu is part of Linux.
The updates are provided by the distribution maintainers. You can usually update through your distro's package manager (if it has one). Major updates may be made only between releases and you may have to completely reinstall to update.
No.
Ubuntu is a Linux distribution (as in a specific OS setup with the Linux kernel.)
Yes.
Scientific Linux is a Linux distribution. It is a free and open source operating system and aims to be as close to the commercial enterprise distribution as possible.
A server with a Linux distribution installed on it.
Many Linux distributions are intended for home users.
No Linux distribution is currently made for any PalmPilot model.
Linux Security Tool Distribution (STD) is really good.