Finally figured out what was causing AE CS4 to run so slow. I'd been having problems with the most basic of compositions; AE slowing down to the point of non-operation and RAM previews rendering and playing back at about one frame per second, even if the composition consisted of a simple animated solid with a circular mask (I meant it when I said "slow"). After scouring the web, uninstalling, reinstalling, testing OpenGL settings, page cache settings, testing RAM modules and generally driving myself crazy, I finally generated the right set of keywords in Google to pop up this:
Apparently if you have the Matrox MX02 installed it generates an AE CS4 plugin called "mveaepreview.aex" that will wreak havoc with AE CS4 if the actual MX02 hardware is not connected. CS3 worked fine though it might just generate the plugin in the most recent version installed.
After moving that plugin to the desktop, CS4 worked like a charm. Just thought I'd share since there isn't currently much out there about it.