Trick Mavericks into letting me use Windows 7 for Boot Camp
This one:


  Windows cannot be installed to this disk. The selected disk has an MBR
  partition table. On EFI systems, Windows can only be installed on GPT
  disks.


Can be worked around like this:


  Using the Bootcamp assistant, revert the HD to a single OSX partition
  layout. Then use the Disk utility to shrink the OSX parition, leaving
  "free space" for the planned Windows installation.


Then, boot from yor Windows USB stick ("EFI boot") and select the free space as target for the installation.

This worked for me.

Regarding Windows 7: I don't know. I'd like to install Windows 7 as well...