Using the VSS version 6.0d that comes included in Visual Studio .Net 2003 in our MSDN subscription, I was able to do an unattended installation but running this EXE in the same folder as the Setup.exe
\VSS\smsinst.exe /k 0123456789
Note: The 10-digit number is the key (ie 012-3456789)that comes with your CD. for the MSDN flavour, the key is in a HTML file at the root fo the disk.
This will install the whole thing. If you want to customize you might be able to edit VSS\SETUP\VSS98STD.STF file the same way (using Acost.exe)as it is described in Visual Studio 6.0
GOTCHA: For this to work, Setup.exe must be able to change VSS\SETUP.TDF Since you will most likely be installing from a CD or a network share the installation will fail without a hint of why (no error messages or log files, Thank you MS!) I had to create a script to copy the installation files to the C:\temp, attrib -r SETUP.TDF and then it ran like a charm.