I install both MS VPC 2004 and its Service pack the same way.
RAR up your install files for the original app. SFX it into an exe with the following comment;
CODE
;The comment below contains SFX script commands
Path=c:\VPC\
Silent=1
Overwrite=1
Setup=msiexec /i "C:\VPC\Microsoft Virtual PC 2004.msi" /qn pidkey=xxxxxxxxxxxxxxxxxxxxxxxxx allusers=2 username="YOUR NAME" organization="YOUR ORG" installdir=d:\Coding\VirtualPC2004
This will silently unpack to c:\VPC and install.
You then need to remove C:\VPC - I use a cmd file as I could't get WinRAR to do it (I also could not get the install to work by unpacking to the "Temp" directory hence this method).
You then have MSVPC installed - If you want to install the SP do exactly the same but you MUST use EXACTLY the same comment file.
Note: you need to insert your own PID-without hyphens, username, organisation name and install directory (where you want it to go!)
I did try doing this using 7zip but it just would not work - go figure. I believe it is related to the temp dir problem.
Strangely (or perhaps not for MS) the RAR file for the app comes to around 15M and the SP 25M !!!