I'm guessing your current drive is MBR. I believe the diskpart "list disk" command will show if a drive is GPT or not.
Diskpart will indeed, but it is not the most informative thing that I have ever seen. The output is
DISKPART> LIST DISK
Disk ### Status Size Free Dyn Gpt
-------- ---------- ------- ------- --- ---
Disk 0 Online 75 GB 0 B
If Gpt is blank, then no GPT. However, if you go into Control Panel - Administrative Tools - Computer Management, select the Disk Management screen, right-click on the disk part (little box on the left, not the volume part) of the picture of the drive, and select Properties, you can read the "Partition Style" property in plain whatever-language-you-have-localized. Mine says "Master Boot Record (MBR)," which is pretty easy to read.