Unfortunately most levels can't be completed due to the changes in black balls, or because of crashes on level completion before progress is saved.

To skip a level, exit the game and then edit the registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\2dboy\goo\profiles\yourname

or on Vista:

HKEY_CURRENT_USER\Software\Classes\VirtualStore\MACHINE\SOFTWARE\2dboy\goo\profiles\yourname

Definitely worth it to see some levels that got cut, and early versions of some others.

to skip GoingUp:
default,HelpMeUp,default,2,GoingUp,HelpMeUp

to skip HelpMeUp:
default,Jengoo,default,3,GoingUp,HelpMeUp,Jengoo

to skip Jengoo:
default,JawBridge,default,4,GoingUp,HelpMeUp,Jengoo,JawBridge

to skip JawBridge:
default,EconomicDivide,default,5,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide

to skip EconomicDivide:
default,ImpaleSticky,default,6,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky

to skip ImpaleSticky:
default,OutOfThePit,default,7,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit

to skip OutOfThePit:
default,HangLow,default,8,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow

to skip HangLow:
default,HungryHungryHills,default,9,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills

to skip HungryHungryHills:
default,FlyAwayLittleOnes,default,10,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes

to skip FlyAwayLittleOnes:
default,DrillBit2,default,11,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2

to skip DrillBit2:
default,Liftoff,default,12,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff

to skip Liftoff:
default,DrillBit,default,13,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit

to skip DrillBit:
default,TheJungle,default,14,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle

to skip TheJungle:
default,Demolition,default,15,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition

to skip Demolition:
default,StraightUp,default,16,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition,StraightUp

to skip StraightUp:
default,Juicer,default,17,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition,StraightUp,Juicer

to skip Juicer:
default,BigRavine,default,18,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition,StraightUp,Juicer,BigRavine

to skip BigRavine:
default,CogInTheMachine,default,19,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition,StraightUp,Juicer,BigRavine,CogInTheMachine

to skip CogInTheMachine:
default,ZeArena,default,20,GoingUp,HelpMeUp,Jengoo,JawBridge,EconomicDivide,ImpaleSticky,OutOfThePit,HangLow,HungryHungryHills,FlyAwayLittleOnes,DrillBit2,Liftoff,DrillBit,TheJungle,Demolition,StraightUp,Juicer,BigRavine,CogInTheMachine,ZeArena

ZeArena is the last level.

Hi im on WinXP 64bit SP2 and i cant find the registry, do you know where it is?

Found it:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\2dboy\goo\profiles\yourname

I need help for skipping them in  801 version or that 800 version that was at the 7 of 7 world of goo wasnt build in a day ttopic