I agree with Aging Technogeek, I always give 20 GB to mint (or any other linux), I did this when I installed mint a year and a half ago and I still have ~7 GB available, because I have a win%&/ XP virtual machine of 6 GB. What I did with my TB HDD is the following:
1 200 GB NTFS partition for music only.
1 200 GB NTFS partition for videos only.
1 200 GB NTFS partition for Misc. data.
1 330 GB ext3 partition for back up. (Including journal it uses ~6 GB but is safer than NTFS)
I used NTFS since the filesystem is only 80 MB, but I'm well aware it's not the safest nor the better place to back up important data, because of fragmentation and because it can be accessed from win%&/, but it's small enough and win%&/ compatible (pros and cons). The ext3 partition is to back up important data since It has a better permision arquitechture and is less likely to become fragmented also thanks to the journal it's less suceptible to become corrupted in the event of power loss, and as I said if you set that only a specific user can view and edit data, even if you boot from a diferent linux only that user will be able to view and edit data, something that I truly like (Of course if you can overide these permisions via root but it's a little bit more secure
). Well that is my suggestion hope it serves you to make a decision.