It's highly recommended to use a password for your user account, for security reasons! There is a way to configure Tasks using a blank password, but I wouldn't recommend it. Create a password for your user account.
>> Just wondering why to automate a one day a week task, I have to now enter a password several times a day.
You can configure automatic logon to your user account upon startup, so that you don't have to enter the password everytime. Use these steps:
Click Start. In the Search box, type control userpasswords2, and then press ENTER. Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
Clear the Users must enter a user name and password to use this computer check box, and then click Apply.
In the Automatically Log On dialog box, type your password, and then click OK.
In the User Accounts dialog box, click OK.
After you restart your computer, you will be able to log on automatically.
REF: http://windows.microsoft.com/en-us/windows-vista/turn-on-automatic-logon