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)
She's at work. You will find her at the end of the game.
the leaf blower is at gregs garage
in 325 North Main Street.
Use it to open the laundry room door at Gregs house.
next to gregs house if not honestly i dont know
5th lockers from the broken locker go to the right
When you unlock Gregs locker the guide is in there
You go right and keep following gregs brother till you get to the school
it is in gregs garage after you kick rodirick out by turning off the lights
Past Rowley's House to the left
to the right of main street also known as the place where your blimp lands
she's not there in "Wimpy Wonderland". She only appears after you beat the game and after you do the sledding mini-game.