To get into the garage at Greg's house, you have to get Rodrick to move his van. But you cannot enter his room while he is playing music -- you have to turn off his power, using Rowley's Joshie card to open the laundry room door.
This continues the game after you follow Manny's trail out of the house to Rowley's, then chase him left to the school. You will retrieve the Twisted Wizard guide from Greg's locker, then take it back to his house to play the game. When you return the game CD to Rowley, he gives you his Joshie club card. Use it to open the laundry room at Greg's house and turn off the power to Rodrick's room. When he leaves, get the dog bowl from his room, then go outside and you can enter the garage.
(see the full solution at the related question below)
the leaf blower is at gregs garage
in 325 North Main Street.
She's at work. You will find her at the end of the game.
next to gregs house if not honestly i dont know
5th lockers from the broken locker go to the right
Use it to open the laundry room door at Gregs house.
You go right and keep following gregs brother till you get to the school
When you unlock Gregs locker the guide is in there
Past Rowley's House to the left
to the right of main street also known as the place where your blimp lands
it is in gregs garage after you kick rodirick out by turning off the lights
In the tree to the right of the school is a scrap piece of paper with numbers on it. This is the combination.