The driver for the 1150 is either built in to Windows 7, or will be delivered to you via Windows Update, as stated on the HP website.
To ensure the driver is delivered via Windows Update or Automatic Updates, make sure the printer is connected to the PC, connected to the mains power socket, and is turned on so that Windows Update can detect it.
If Automatic Updates are disabled, you can run Windows Update manually via "Control Panel >> Windows Update"