All effects in a default install are located in the flightdata.cat. When you installed the 2008 patch, all the .cat files were overwritten with newer versions.
Hence, you cannot go back to using the "old" ones, unless you're willing to go through a rather long and tedious process. And that involves uninstalling the entire sim, installing and patching it to the previous ('06) patch level, extracting all the necessary effects tga and particlesystem files, placing them into the appropriate folders, and patching the game back up to the '08 level.
This assumes, of course, that you're knowledgeable enough to understand exactly what's involved, and what you're doing. And even then, you may run into some issues, as the newer graphics.dll demands some editing of the aforementioned particlesystem.ini...so you may wind up going back to square one.
Best solution? Either tone down the graphics, or upgrade your system, or don't install the '08 patch.