I am using Cakewalk 5. I just downloaded a bunch of sounds, synths, and effects to (hopefully) use. They are all fxp files. I put them in the plug-ins folder with all the other vsts & synths, but they are not showing up when I use cakewalk. How do I use these? Do I need to update to cakewalk 6?

Welcome to the forum.
According to the MC 6 Help file, FXP files are presets, not VST synths or effects, so the Plug-in Manager won't see them as synths or effects.
Where did you get the files?

right, FXP files are presets for VSTs or VSTis, not synths or FX themselves.