I was under the impression that there isn't a way to root ZVJ... so I don't think following the directions in the link provided will get you very far...
There is a workaround however - the Optimus S allows firmware downgrades, by downgrading to ZVH or ZVD you can attain root - you can then upgrade back to ZVJ while retaining root if you so choose, or you can remain on ZVD (I wouldn't advise staying on ZVH, but it's easier to root via ZVH if you want to use ZVJ, rather than staying on ZVD after reverting)
rooting via ZVH is covered in this sticky thread:
http://forums.androidcentral.com/lg...75303-how-root-stock-zvj-downgrading-zvh.html
and rooting via ZVD is covered in this sticky thread - take note that you will need to first revert to ZVD (which requires a data wipe), links are provided, but this thread can be a bit much to take in... the process is essentially the same as in the previous link, but using ZVD update.zip (should be able to find links directly from Sprint for it) and just rooting ZVD (no updating afterwards)
http://forums.androidcentral.com/lg...ls670zvd-zvh-100-automated-zvj-automated.html
And heading off the next question, maybe?
What's the difference?
ZVD is Froyo, ZVJ is Gingerbread, if you're going with a custom ROM though, more are made for ZVD, but there are patches to allow you to use either radio version.
Also reverting to ZVD requires a data wipe - so you'll be losing all your apps, data, etc, whereas going the ZVH route doesn't require a data wipe - and while a data wipe is still advisable (and required before going to a custom rom anyhow...) taking the ZVH route will let you get TitaniumBackup or similar installed to backup your apps before you have to wipe them - of course, flipping around with firmware versions like this... I've not heard of problems with apps being corrupted and such, but it's not outside the realm of possibility... so I wouldn't count on your apps data integrity through this process, even though most people report things going fine.
If your current apps and data don't matter, and you'd rather not have to patch after installing custom roms, you might want to try the ZVD route... I haven't checked the links for that in awhile though... the ZVJ root package should contain all the stuff for rooting ZVD too (I think?) but the menu options might be a bit different?