My machine is currently running Windows 7. I have 2 partitions: OS (C:) and DATA (D:). I intend to do a native Ubuntu 14.04 install. Assuming I format my Windows OS partition, will I have full access to my D partition in Ubuntu ?
Others have posted good information; however, there's one other critical detail: Ubuntu lacks a useful NTFS repair utility. Filesystems occasionally become damaged. Power outages, bugs, system crashes, and other conditions can cause this to happen. When Ubuntu encounters a damaged NTFS volume, Ubuntu will refuse to mount it. Thus, on an Ubuntu-only system, using NTFS on an internal disk is a problem waiting to happen. As soon as that NTFS volume becomes damaged (and it will), you'll have to move the disk to another computer or use a Windows emergency disk to repair it. Either action is a hassle and even creates new risks.
Thus, if you intend to have an Ubuntu-only system, as it sounds like you do, I strongly recommend converting that data partition from NTFS to a Linux-native format. You can do that by backing up, converting, and then restoring the data; or by creating Linux-native storage, copying the data, and then converting the NTFS to Linux-native for use in some other way. (You could also copy the data and then resize the Linux filesystem, but that creates new risks, so I only recommend doing that if you've got a good backup.) The best approach really depends on how much data you're talking about, how much unused disk space you've got, and how much backup capacity you've got.
I'll take this opportunity to step onto a soap box and say that if you don't have good backups, you should make them, even if it means buying external storage for backup purposes. Every few days, I see a tale of woe from somebody who doesn't have good backups and who's lost irreplaceable data as a result. Please don't become one of those people! If a conversion from NTFS to a Linux-native format helps convince you to buy necessary backup hardware, then that's another advantage to doing the conversion.
Ubuntu can certainly read and write files in an NTFS partition. The data partition needs to be mounted. This can be done automatically on bootup by modifying the file system table (/etc/fstab). See, for example, Mounting Windows Partitions in Ubuntu
Yes, out of the box. However, I would advise to avoid a lot of writing to it, sinse Ubuntu will allow you to create files with names that Windows can't read - names with symbols and weird characters. You will be able to rename them from Ubuntu later.
Next, NTFS does not support Linux access rights, so you will not be able to place root or
/home folder on it.
NTFS driver is yet not 100% good.