Really your just looking at 3 different Linux Distributions with 2 versions each.
At the heart, they are all Linux OS. Different companies like Red Hat but together the linux installation in different ways, the biggest differences between them are the look of the installation , the packages that they offer, the package management system, and the look of the default GUI.
any of these OS's will run the Apache OS and the PHP Processor. All of them will also run a mySQL Database server.
I've used Red Hat and Ubuntu in the past, and don't really have a preference between the 2, both are easy to use if you are familiar with the Linux environment.
It is posible to make a Connection to a MSSQL Database in PHP, but This is not supported in Dreamweaver, nor do we support using a MSSQL Database. Dreamweaver will only allow for connecting to a MySQL Server.
