Wow, the thread resuscitated!
OK, MBR. What do you want to use the drive for? If you want to install some version of MacOS and/or clone an existing bootable MacOS drive and boot from it, needs to be in GUID/Apple Extended format. Else if you want to be able to exchange files from Windows and Macs, it will need to be in MBR and either FAT32 or ExFAT format. Cannot use Windows' MBR/NTFS cause Macs can't deal with it.
Once you have selected a partitioning scheme, the Options... button will be enabled and there you will be able to choose the partition/format scheme.
Note that in recent MacOS versions (ElCap, Sierra, etc.) the Disk Utility window is very different and behavior is quite wackier.