The extracted boot image is usualy an .IMA file. The boot section is not part of the user data, that's why you don't see it listed.
You need the bootable image for your specific needed disc, you can find some here http://www.bootdisk.com/bootdisk.htm Ectract the .IMA from the .exe with an arhive tool like WinRAR.
I don't know why you need to make that bootable partition...
If you follow the guide to make a bootable image you should get there.