I do recall that the Lyrical Distortion install was a bit messy, perhaps compounded by the fact that I bought every one of them at once.
Installing libraries that aren't blessed by Native Instruments consists of simply copying files and folders, and making sure the samples are where the instrument definition file expects them to be. Sometimes, you'll get libraries from amateur library creators who mistakenly define their instruments with absolute paths to their samples, in which case you have to redefine the instruments yourself. I don't recall LD being
that complicated, though.
What you want to end up with is a folder for each instrument. Within that folder you'll have one or more .nki files and a subdirectory containing the samples. So, for example, one of the instruments is called "Ripper - Direct". I have a folder called "Ripper - Direct". It contains "Ripper - Direct.nki", the instrument definition file, and a sub-folder called "Ripper - Direct Samples".