If you are setting up a x64 server for MOSS, there are some things to be taken care of. I ran into couple of issues while setting up my development machine and had a hard time debugging it.
%systemdrive%\WINDOWS\Microsoft.NET\Framework64\v2.0.50727
If you are in habit of using 32 bit version for long time, you might mistakenly use the one located at %systemdrive%\WINDOWS\Microsoft.NET\Framework\v2.0.50727.
Note that this directory is present even if you only install X64 version of .NET Framework for compatibility reasons. But running this command would only give you error unless you enable 32 bit worker process on the IIS. This can be done by setting the following value in IIS metabase from the command prompt.
cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64
%systemdrive%\Program Files\Microsoft SDKs\Windows\v6.0A\Bin\x64.
This point is worth mentioning because, VS 2005/2008 by default sets the PATH environment variable to 32 bit binaries regardless of the architecture.