NFS5 - Porsche Unleashed and nvidia cards don't seem to get along regarding the text. With the older cards and any ATI video card, you can turn up the ansiotropic (filter) to solve this, but with the newer nvidia cards, it's an issue.
You can try DX8Z.DLL from the spot patch, this may help with the text, but may mess up the actual game play. I have a copy of the spot patch, intended for NFS4 - High Stakes, but the drivers are interchangeable. Note that you only need to extract DX8Z.DLL from the zip file, the rest of the stuff is for NFS4. Backup your DX7Z.DLL, extrack DX8Z.DLL, and rename it to DX7Z.DLL.
spotptch.zip