you shouldn't need to download the lwjgl source jar, the full slick download comes with all the dependancies its needs (unless you are using an OS other than windows in which case you'll have to grab the natives for that version of lwjgl), you just need to add the lwjgl.jar to your external jar path.
You are correct, the JWGL is inside the Slick. But regardless, both the jar files and the.Java files misses classes like GL11 for example. I placed all jars in the same place where I placed Jogg and Jorbis jars that I used from before but I cannot import certain classes because they do not exist.
Also, downloaded GL11.java from the Internet but when I compile I get
"GL11.java": illegal character: \64 at line 717, column 22"
"GL11.java": <identifier> expected at line 717, column 50"
example of methods that give error.
void glAccum(@GLenum int op, float value);