I have been searching through the archives for information on how to install adjustable coil-overs on a 240z, as im interested in installing 17X8 and 17X9 wheels in the future. I have read that the strut inserts (?) have to be shortened. From my previous experience with suspension installations the "strut inserts" were always just referred to as "shocks". I am kind of unclear on the descriptions of "strut cartridge," "strut housing," and "strut insert". and since im not clear on what exactly these parts are im also unclear on what part is actually cut up to be shortened. Could someone on here with more knowledge enlighten me? Thanks in advance.

Strut cartridge, insert and shock are different terms for the same thing.

They are installed into the strut housing which is what the lower spring perch is welded to.

ok, that cleared things up somewhat, thanks, is it the strut housing or strut insert that is cut shorter? i would assume the strut insert? (sorry i'm really in the dark about this and am trying to figure out how to do this)

You will have to cut the strut housing in order to fit the cartridges you get.

Here's a Tech Article that should answer nearly all your questions. In the middle of the article it explains shortening the housing.

http://www.classiczcars.com/forums/showthread.php?s=&threadid=1200