Standard software (like traditional Office 2003) writes hundreds of entries into the Windows Registry, installs shared DLLs in System32, and buries activation tokens deep within the OS. This means you cannot simply copy the "Program Files" folder to a USB drive and run it on another computer.
Manually download and install Office 2003 Service Pack 3 (SP3) and the Compatibility Pack (to open .docx and .xlsx files). This is the "fullness" that most repacks miss. installs shared DLLs in System32
Run your virtualization software to take an "after" snapshot. It will compute the differences: new registry keys (roughly 3,500 of them) and new files (approx. 450MB). installs shared DLLs in System32