How to reinitialize a hard disk drive?

Ok, here's the problem:

 

I initialized a new hard disk drive with a GUID (GPT) partition table (it was a mistake) and I need to reinitialize it to get a MBR partition table. I know what I did is stupid but I'm pretty sure it can be fixed quite easily. I initialized the disk with Windows Vista but I can't reinitialize it. There's simply no option available. I guess I'd need another program to do it.

 

Thanks for any useful input.