A troublesome achievement in some ways.
You'll have to do the tracking yourself.
This faq guides you through all the secret rooms and hidden green jewels:
http://www.gamefaqs.com/xbox/557315-rayman-3-hoodlum-havoc/f...This old site shows the secret rooms with pictures should the above not suffice:
http://rayman.bonusweb.cz/pok2_wantedrayman/rayman3/pok2/tip...These are not all the Jewels but other ones will not be hidden away.
Specifically hard to get:
The Tower of the Leptys Part 4: 4 green jewels
On your way up to the final boss is a hidden door. The requirements for this door to open are unclear since the game came out. According to faqs I read it's either connected to your total gamescore or the score from the first 3 parts of this chapter.
When I got acces I scored 100%, 96% and 100%. This score pulled me over 400.000 gamescore before I entered part 4. Therefore I cannot conclude which one of these options opens the door but I suspect it's the 400.000 gamescore. If anyone had clarification on this let everyone know in the comments.
The last one is hidden during the boss fight. It's during the part where the blocks are up in the air and you'll find yourself on a round platform. In front of you is a small gap. You will have to drop down and land on a ledge. Follow the ledge to an emerald and return with the yellow powerup. If however you fall off the grid you'll die and you will have to start all over again. So it's through the gap NOT down the sides, the camera won't help you at all so helicopter down while hugging the wall and you'll make it.
Note: I found the green jewel during the final boss fight before I got access through the secret door in this level. I finished the game, upped my level scores and returned to this part. When I got access to the secret room I collected the four jewels but the achievement didn't unlock. As soon as I collected the final jewel during the bossfight again it did unlock. So if this happens to you try to do that before throwing your controller against your wall. It may mean that you have to collect every jewel there is in a level (probably counts for every level) as this seems to happen to the Tribelle and Matuvu achievements too
Ones that are also troublesome:
*The summit beyond the clouds Part 3 - during the snowboard trip near the end a green jewel can only be earned by taking the high road, jump in the middle and catch it during the fall. If you fail be sure that Globox finishes first; that way you'll start back on the top. Good way for 100%ing it
* Edit thanks to Kmetalmind in the comments - ' There´s a hard to get jewel on Desert of Knaaren Part 6 (just the one where the two annoying big flying hoodlums attack you). You have to kill all bomber hoodlums on tilts before breaking the cage, by using their own bombs to make them fall from their tilts. Then you get a greem gem instead green power.' This one is also explained in the Faq but its tricky. The teensies in the cage in the back will give you a green powerup but when the enemies are all gone they'll give you a green jewel. It's right before the secret area behind the campfire.
The faq above should suffice for most of the green jewels. Some other ones you'll get from teensies or found elsewhere. You can also try this walkthrough that's posted in the 100% achievement guide:
http://uk.faqs.ign.com/articles/432/432233p1.htmlgood luck