Wizards of the Coast Character Builder full version including April 09 update!

Double-Click on 'CharacterBuilder_Setup.exe' which will install the charter builder and all dependences 
execute CharacterBuilder_Update_Nov_2009.exe and make sure it points to the directory where you installed Character Builder ('C:\Program Files\Wizards of the Cost\Character Builder' by default)

You can also use 700_DDI_CB.exe to download the CharacterBuilder_Setup.exe and install.  This method will also update the Microsoft .NET framework if that step is necessary for you.

I've heard that certain versions of Windows Vista can have issues with this.  If yours doesn't work after attempting to apply the update, try the following:

Go to the CB direcotry, Right-Click RegPatcher.exe and select "Run as Administrator"

It should work then.