"Select CD-ROM Boot Type" on 2007 imac windows 7

You need to use Bootcamp Assistant. Unfortunately Apple has updated all of their support articles for installing Windows 10, so you may need to use the Internet Archive to get a copy of the old Apple articles.

Here is an old post on the Microsoft forums for installing Windows 7 so it may provide you with a general guide.

https://support.microsoft.com/en-us/topic/installing-windows-7-on-your-mac-using-boot-camp-8d9df954-f2c0-2bf9-c400-2b21eb58ec6f

Here is a current Apple Bootcamp article (unfortunately it doesn't go back to the age of your system, but maybe you can use it to access an older copy in the Internet Archive).

Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support

Download and install Windows support software on your Mac - Apple Support

Keep in mind that Microsoft turned off the Windows Activation Servers so you won't be able to activate any Windows installations.