Just go to program files>Image Line>FL 8>Plugins>Vst and drop the dll's in there, or if they come in exe just install it to the same directory. Than when u open FL Studio ur gonna go to the channel drop down screen go to "add one" and than click on "more". From here you are gonna click on fast scan thats located onn the bottom of the pop up window showing all your vst's
You'll find a lot of the same ones within these links, but just go through them. There's a lot of good ones. That first link might have most of the best freeware, but I would still go through all of those links.