Under Windows:
- Grab the Windows 7 Home Premium x86 SP1 U ISO.
- Follow these instructions to prepare a USB drive.
- Use the Windows 7 USB/DVD Download Tool to copy the ISO to the USB drive.
Under OS X:
- Run the Boot Camp Assistant.
- Check "Install or Remove Windows" and create the Windows partition.
Under Windows Installer:
- When prompted for installation type, select a "Custom" installation.
- When prompted for partition, select the "BOOTCAMP" partition, but before continuing:
- Click "Drive options" and then "Format".
- Continue with the installation.
Under OS X:
- Use Disk Utility to format a thumb drive as FAT32.
- Use Boot Camp Assistant to download Apple's Windows support software to this thumb drive.
Under Windows:
- Install the Windows support software from the thumb drive.