According to the VS 2005 website:
Before you install
The Visual Studio 2005 Beta 1 Refresh is the same as the previous beta release, but now includes a Community Technology Preview (CTP) of Visual Studio 2005 Team System. While betas receive a much higher level of testing and feature work, CTPs are intended to expose developers to the latest working build. The Visual Studio 2005 Beta 1 Refresh is therefore still unsupported pre-release software and there are some precautions you should take. Please make sure you read both the Visual Studio 2005 Readme and the Visual Studio Team System Readme prior to installing this release.
For me, this means that if I currently have Beta 1 installed, there is no reason to uninstall it and then reinstall the same thing from different setup files. But, if I had downloaded the CTP of VSTS several months ago, then I may want to install that because the VSTS is new bits.
Maybe this will help someone who might think that this is a Beta 1.5 build.