Whenever I try to start a new file or open an existing file I get the message
Microsoft Visual C++ Runtime library
I have read dozens of comments about this issue and tried everything, I have Core Duel Quad processor XP SP-3 alle updates, 2 GB RAM, I ereased all preference files. Photoshop works fine, Dreamweaver too.
I had many years Illustrator 9, worked fine, now I want to try CS4.
Runtime errors usually point to driver conflicts/ conflicts with other software. In your case possibly simply the PDF libraries already installed by Photoshop are causing issues. I recommend you simply use the CS4 Clean Utility to unregister your other installs, then try to re-install Illustrator. For other potential causes, we need more info. Graphics card? Graphics tablet? Printers? For the latter two, uninstalling them or at least disabling them may allow Illu to launch...