When installing SQL Server 2005 64-bit on Windows Server 2003 x64, the installation of SQL Server stops in the very beginning when SQL Server installer tries to install .NET Framework 2.0. .NET Framework 2.0 is a prerequisite for SQL Server, so the installation halts and you're unable to proceed.

Also the SQL Server installation logs (in %ProgramFiles%\Microsoft SQL Server\90\Setup Bootstrap\LOG\) say things like:
Failed to install.NET Framework 2.0 E:\Servers\redist\2.0\dotnetfx.exe: (216) {t:\yukon\sql\setup\sqlcu\dll\customcomps.cpp:354}
SCU_SetupMgr::svc() caught exception: Failed to install.NET Framework 2.0 E:\Servers\redist\2.0\dotnetfx.exe: (216) {t:\yukon\sql\setup\sqlcu\dll\customcomps.cpp:354}. SetupMgr: state=ERROR, cancel_state=0, is_done=0, ActionRequired=1, NeedReboot=0, custom_props={AutoStart=true
Thoughts:
Apparently the version (still) coming with SQL Server 2005 64-bit version is not compatible with 64-bit versions of Windows.
Solution:
- Install .NET Framework 2.0 x64 separately (download it from Microsoft)
- COPY SQL Server files from DVD to hard drive
- RENAME the two instances of dotnetfx.exe files to anything, e.g., "dotnetfx.bak"
- Restart SQL Server installation (the installation will ignore .net framework routine)