Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Mandriva has quite a reputation for creating Linux distributions well suited for beginners coming from Windows. They have several paid-for versions but with the release of Mandriva 2007 a free version has been released.
A free Live CD has been available for a while but this version includes more software. This can be downloaded as three CD images or as a single DVD.
Installation is simple and Mandriva has one of the best hard disk partitioning tools of all Linux distributions. All the partitions on the disk are shown graphically and Windows partitions can be resized to make enough space. This takes most of the stress over what can be a dangerous part of installation.
There is a good selection of software included in this distribution including the latest version of Open Office.