How to Unlock World Seven on New Super Mario Bros. DS: 5 Steps

Now, most people who have New Super Mario Bros. really want to go to world seven. If you have the Wii version, this may help, if it doesn't, well, sorry.
STEPS

1

GO TO WORLD ONE.

2

COMPLETE LEVEL 1-4 TWICE.

3

THIS IS THE TRICK: on level 1-4, you can get a mini mushroom. If you have done the level already, you probably know that. Get the mini mushroom and don't loose it. Complete the level.

4

THIS NEXT STEP IS UNNECESSARY BUT MAKES GETTING TO WORLD SEVEN A WHOLE LOT EASIER: Repeat Step Three.

5

GO TO THE CASTLE LEVEL ON WORLD FIVE AND BEAT THE PLANT GUY. Finish as a mini, and you'll get to world seven.
TIPS
The trick with this is, you only have to FINISH as a mini. So, if you are a fire power, be that, beat the plant, and then change to a mini and get the key.
WARNINGS
World Seven is hard, confusing, and made of clouds. The boss is a giant Lakitu (the guy who throws spinies at you on world two) who has a storm cloud for a lower half and blasts you with lightning.