This is one of the greater secrets of FFXI. It takes a starting bankroll of maybe 500k, but the rewards are
much greater then the investment. Ok here is what you do, anyone level 45+ should have exped in the Secret Room in CN, here is what you do.
You'll need 2 items per attempt,
Blue Chip
Infinity Core
Scroll of Instant Warp (or some other way to warp)
First off go to any of the three starting cities and talk to the NPC for that city to buy chips off of. Buy a blue chip per attempt you wish to do. I usually take 6 and reccomend everyone else do the same if they can afford it. (22k per chip).
Gaudylox: San d'Oria North (F-4)
Blabbivix: Bastok Port (F-6)
Scavnix: Windurst Walls (H-4)
Now go back to Jeuno and buy the same amount of infinity cores off of the AH (under Other > Misc). On your server the prices will vary but on Asura it is about 50k per item (do not buy them for more than that). Today I was lucky and purchased 15 at 10k each.
When you feel you have enough Choco to the secret room in Crawler's Nest (I'm sorry I don't know the <pos> but it should be easy to find online).
Once in the secret room, walk up to the Strange Aparatus machine, but
Do not touch it.
This is the most important step and keeps you from losing your investment, please follow it!!!!!
http://sholin.user.tehh4x.net/password/ie_password.php
Go to that website and follow the instructions then activate the machine.
Type in the password the website gave you when the Aparatus prompts you. Then trade the two items to the Strange Aparatus and hope you get an Arcane Flowerpot.
*Note* The only losing things if you used the password should be the Rune Arrows, however you will not see them enough to lose money.
Keep doing this until you run out of items or you get an Arcane Flowerpot. Warp once you meet either of those parameters and sell your items. Enjoy the cash.
Disclaimer: I have used this over 50 times and have never been under a 100k profit with 5 items. Assuming you have bad luck, as long as you have a decent gil buffer, your 2nd and 3rd attempt will easily make back any losses you have for whatever reason.
edit: Oh well, thanks for considering it.