The MBR layout has a 2TB limit the capacity that is left over will not be addressed so you can not use/see it. You must use GPT for single partitions larger than 2TB to be recognized on Windows (WinXP x64-bit and up support GPT). <-Now to get around this problem by using MBR w/ FAT32.
When you use the MBR layout seeing 1.6TB on ^2Tb drives is normal, open up the 3rd-party app I suggested and format it to FAT32. Make sure to lower the cluster size. Once done Windows will now recognize the full capacity and you will see 3.63TB in FAT32 format. You can now create unallocated space and create further partitions from there.
Here is a screeny of what you are trying to accomplish (fully tested and works on PS3). Please pay attention to Disk 2.
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