I realize that Vista (I am running Vista Ultimate) came with its own "upgraded" version of DirectX 9.0. Should I install the latest DirectX 9.0c (June 2007 version) on my Vista Machine? It is confusing because this machine has DirectX 10 and 9 on it.100% of my games are DirectX 9 games.

MS protects itself from such glaring errors by not allowing the installer to run unless it is appropriate for the computer.Donwload the June redistributable, and try running the setup. If it runs, it's right.Allcott

You are very safe with updating DirectX, even with old versionsas noted. My son bought an old computer game that crashed immediately with a missing dll on startup. I recognized this asa DirectX component, so installed something like direct X7 overdirectX 9.0c. Program worked, and there was no effect on FS.Tom