Description in-game, Scroll down for people who finished.
Idea thanks to www.notpron.com, an amazing online riddle game.
Hints:
Level 1: If you need a hint here, give up now.
Level 2: Seriously...
Level 3: First find the button to bring you to the input bar. Look into the background; what do you usually hang in a closet?
Level 4: Notice how you can highlight the level number.
Level 5: The "key" is so small you can't even see it under normal conditions.
Level 6: The painter drew her without something... Use his first name only.
Level 7: Emphasis on the word "Dutch" [u]ghost[/u].
Level 8: Kind of like synonyms!
Level 9: "Cat's Purr"
Level 10: Didn't he have 3 uncles?
Level 11: I like this song, but how does it go?
Level 12: You need to get to level 7 at www.notpron.com.
Level 13: It's an anagram.
Level 14: Notice how numbers are spelt using [i]numbers[/i].
Level 15: Similar to Level 11.
Level 16: I nicknamed this level "Cheaters Paradise" =P.
Level 17: That's fon't almost looks foreign... Maybe you should translate it?
Level 18: It's a gift level. No hint for you =P.
Level 19: You almost there! Read the last piece of the text over in your head.
Level 20: No more hints, this level's all yours =P.

Alright, I'm just going to add the names I have now, I found a few walkthroughs on the net, and it's not really fair anymore.
Congratulations to:
Nabcat
Neil (darkbuu) Ralls-Whitmore
thom van haren
Ridhi Singh
FlippaxXx
tracy slade
Melissa M
Marina Bianco(x2 =P)
§pårtåkus Mørïårty
Erlend Gram Simonsen
The Remister =P
Justin Lee (Thanks alot!)
angie
Kathrynhhayes
snuffsaid
MEENA27
Adriana de M. V. dos Santos
Delia Ryan
B Flatt
Nina Maria Bleiweis
Hannah Stevens
hannah cook
Jess Teng
sarah alsardi
dalaz777
martina rurali
Zelda_Sword aka Jeff (Congratz =P)
Khmerry Chhor
Nicola Calvert
hydra23
Jaap Qualm
Doony Brasco
Mark Vogan.

Congratulations to everyone who legimately won the game, sorry it took so long to add you to the list.(I'm supprised I didn't run out of room =P!)I hope you had fun, and keep your eyes open for number two =P.