Was this during the install phase, or post-install?
It is possible that you might have to pass some kernel parameters at the second-stage boot: prompt such as:
or a combination to get your screen back. Just hit -tab- at the second-stage to stop the countdown and allow you to type in the parameters.
As a diagnostic, you could also try another distro, such as Feisty 7.04 "alternate". If that works, we can use some information from it, or just keep it.
Being secondhand, that ram could also be bad, or not the right spec even if it looks original. That machine seems to have been "parted out" and perhaps someone just threw in some apple ram from another machine...