Extract the game

OpenNFSPU reads the installed game folder: GameData/, FEData/ and Porsche.exe (version 3.5), or an .iso image of that folder. On Windows, install the game and apply the 3.5 update as usual. On macOS and Linux you don't need to run the Windows setup: get the folder out of the installer instead.

A repack disc image with a RAR installer

Some copies are a single disc image (for example NFS_V.ISO) whose Setup/install.exe is a RAR self-extracting archive of the already installed and updated game (version 3.5). Extract it with unar (The Unarchiver's command line tool; brew install unar, apt install unar):

# macOS: mount the image read-only
hdiutil attach -readonly -nobrowse -mountpoint /tmp/nfsiso NFS_V.ISO
unar -o ~/Games /tmp/nfsiso/Setup/install.exe
hdiutil detach /tmp/nfsiso
# -> ~/Games/Need For Speed - Porsche Unleashed/ (GameData, FEData, Porsche.exe, ...)

On Linux, mount it with sudo mount -o loop,ro NFS_V.ISO /mnt (or extract the ISO with bsdtar) and run the same unar command. 7-Zip and p7zip list the archive but fail on it with "Unsupported Method": use unar.

A retail CD

The retail discs carry the game in the installer's own layout. Install it on Windows (or in Wine) and apply the 3.5 update, then copy the installed folder; at least GameData/, FEData/ and Porsche.exe are needed.

Check

ls "Need For Speed - Porsche Unleashed"
# FEData  GameData  Porsche.exe  ...
wc -c < "Need For Speed - Porsche Unleashed/Porsche.exe"     # 2129965 for version 3.5

For development, put (or link) the folder at ./game in the checkout.

Make an ISO of it (optional)

One file instead of a folder (the launchers and the browser player take either):

hdiutil makehybrid -iso -joliet -o NFS_PU.iso "Need For Speed - Porsche Unleashed"       # macOS
genisoimage -J -joliet-long -r -o NFS_PU.iso "Need For Speed - Porsche Unleashed"        # Linux

On Windows use any ISO 9660 + Joliet tool (ImgBurn, or oscdimg -j1 from the Windows ADK). The image must contain the installed game; see Game data.