Did you just download and tried installing the Feb CTP build?  Did setup complain that it found existing incompatible components?  Along with your dowload package is a tool on the CD that will scan your machine and allow you to remove previous versions of SQL Server components and the dotnet framework.  You can run this tool or you can try removing the previous versions of SQL 2005 or VS 2005 from Add/Remove programs.  The tool is called "Build Uninstall Wizard" and here are some steps to running it:

1. Go to <CTP February 2005 Install Files>\Setup Tools\Build Uninstall Wizard
2. Double-click sqlbuw.exe.
3. Read the "Instructions and warnings." Click Next.
4. In the "Instances to uninstall" dialog box, read the components, the instance names, and the versions of each of the components that will be removed. This is a read-only screen and no input is required. This screen just informs you that these components will be removed. Click Next.
   
   Note: System databases will be saved for SQL Server 2005 Database services only. All other components will be uninstalled.
   
   
5. In the "Uninstall Prerequisite Components" dialog box, check the boxes to allow the Build Cleanup Wizard to remove .NET Framework and SQL Native Client. These components must be removed for you to install CTP February 2005. Click Next. 

WARNING: If there are other applications installed on your machine that require .NET Framework (for example, Visual Studio 2005), those applications may not work correctly if .NET Framework is uninstalled. If you have applications that depend on .NET Framework, such as Visual Studio 2005, you must uninstall those applications before uninstalling .NET Framework. To uninstall Visual Studio 2005, you must uninstall the Visual Studio 2005 components (if any) in the exact same order shown below. (Refer to the Visual Studio product documentation for more details.)

û       MSDN Library for Visual Studio

û       Microsoft Visual Studio 2005 Beta

û       Microsoft Visual J# .NET Redistributable Package 2.0 Beta

û       Microsoft .Net Framework 2.0 Beta

Run the Build Cleanup Wizard from the command line

You can also run the Build Cleanup Wizard directly by running <CTP February 2005 CD Drive>:\Setup Tools\Build Uninstall Wizard\sqlbuw.exe with the following arguments to run in silent mode:

û       /quiet – Required to run silently

û       REMOVEPREREQUISITES=1 to uninstall .NET Framework and SQL Native Client

û       ERRORREPORTING=1 to send fatal error reports to Microsoft in case of failures

û       ADMINPASSWORD=<password> required for cluster installations only

Example command to remove everything on your machine:

<CTP February 2005 Install Files>\Setup Tools\Build Uninstall Wizard\sqlbuw.exe /quiet REMOVEPREREQUISITES=1 ERRORREPORTING=1 ADMINPASSWORD=<password>