The Epson Photo R300 doesn't require the drivers your trying to install. Vista comes pre-installed with what they call In-Box drivers .

The advice from Epson is:

DO NOT INSERT YOUR EPSON PRODUCT SOFTWARE CD IN YOUR WINDOWS VISTA COMPUTER because the setup program is not compatible with Windows Vista.

In-Box = Drivers are included with Windows Vista. Just connect your Epson product to your computer and follow the on-screen instructions that Windows Vista displays to guide you through driver installation.

With this in mind, I'd un-install the drivers you have installed, then follow the above instructions and subsequent prompts.

Good luck.