According to this article you should be able to use GPT with windows 7. You may run into problems reading the disk with some utilities or if you try to read it from a Win XP machine. Using MBR will guarantee it's more compatable with older OS's and utilities.
Did you read the article? The word "article" in my first post is a link. click on it. Anyhow, it says:
5. Is EFI required for a GPT disk?
No. GPT disks are self-identifying. All the information needed to interpret the partitioning scheme of a GPT disk is completely contained in structures in specified locations on the physical media.
The OS needs to know how to read GPT disks, which windows 7 does.