You can tell in Disk Management by right clicking on the Disk #. It will be the opposite of whatever you have as an option to "Conver to (MBR or GPT) disk". Unless your motherboard supports a EFI BIOS (most do not), then you will most like need to use a MBR disk for Windows 7. By default, all hard drives are formatted as a MBR disk unless you manually convert it to a GPT disk.
You can read more details about MBR and GPT in the tutorials below though. Convert GPT Disk to MBR Disk
and Convert MBR Disk to GPT Disk
Hope this helps,