As mentioned in my comment above, I think you're approaching this the wrong way. But, I'll answer anyways.
The task scheduler is an MMC (Microsoft Management Console) snap-in. It therefore requires UAC elevation to run. With Windows 7's default UAC configuration, you won't actually get a prompt for it, because it's a system configuration action. The regular GUI configuration options for UAC don't let you do this, but you can configure UAC to require that you enter the account's password instead of just clicking "OK", and that it prompt for all actions.
If you have Win7 Pro or Ultimate, you can do this from the security policy editor. Run
secpol.msc, and navigate to
Security Settings > Local Policies > Security Options. Find the setting
User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode. Set it to
Prompt for credentials on the secure desktop.
If you have a lower edition of Windows 7, you can configure this in the registry. Open
regedit.exe, and navigate to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System. Find the dword value
ConsentPromptBehaviorAdmin, or if it doesn't exist, create it. Set it equal to
Once this is set up, you will be asked for your password when you run any administrative program, such as the MMC or some control panel applets.