Yup. Windows will not install when there are other drives present that have GPT.
Very old simple to just remove until later.
If you were installing to the same drive as OS X (prefer not to of course) still need to pull the drives temporarily until after Windows is done.
you do not need a new drive. You can just format the drive now that you were going to use:
Disk Utility: Partition: 1 or more, does not matter: Advanced: Options - choose MBR Windows partition table format. Click Apply. Then Apply again.
When in Windows 7, choose the entire drive - Advanced Options and delete what DU created! let Windows do its thing - no need to create or format if you deleted / removed those partitions.