Assume that you have a Boolean variable called Test. Here is how you would set it to True using a Script Task.

1) Create a Script Task.

2) Add 'User::Test' (no quotes) to the ReadWriteVariables property.

3) Modify the definition of Public Sub Main as follows:

Public Sub Main()

Dts.Variables("Test").Value = True

Dts.TaskResult = Dts.Results.Success

End Sub

(Leave the rest of the Script Task code untouched.)

Job done.