Harmy said:

Well, I didn't choose to partition it this way - in the menu when installing Windows and selecting where I want to install the OS, the HDD space already showed up divided into two 2TB chunks of un-allocated space, which it was possible to allocate and two 746.52GB chunks of un-allocated space, which it was not possible to allocate.

Interesting. I guess Windows doesn't use GPT for partitioning during installation.

Are you willing to reinstall? The easiest way to do this is to use a Linux Live CD (e.g., Ubuntu) to do the partitioning prior to installing Windows.