I have recently bought a laptop with an SSD of 128 GB and a HDD of 1 TB. Currently I am running windows 8. Windows is installed on the 128 GB SSD (C drive) and I use the 1 TB drive for data storage (movies, pictures, musis, documents...). This is the D drive. Would it be possible for me to install ubuntu on the C drive and keep using D as my data drive? I don't have enough space to make a backup of my files. What are my options to install ubuntu without losing the files on the D drive? Thanks in advance.
Correct this problem! I've seen too many people who post here or elsewhere with sob stories about how they've lost all their data because they tried X, Y, or Z and it had unintended consequences, or because their hardware failed. These things do happen, and by and large, they happen suddenly and unpredictably. So keep backups!
That said, you can certainly install Ubuntu on the SSD, either instead of or in addition to Windows, and retain access to files on your 1TB disk. (Under Linux, the designations "C: drive" and "D: drive" are meaningless. Even under Windows, these terms refer to filesystems, which don't necessarily correspond with physical disks in a 1:1 manner.)
If you intend to replace Windows, though, I strongly recommend converting your data disk from NTFS (which it probably uses now) to a Linux-native filesystem. This action will require either a multi-stage process of moving file and resizing partitions or a backup-and-restore operation. As resizing partitions is particularly risky, a backup is highly recommended for the former procedure, at which point you might as well just do a backup-and-restore. Anyhow, although Linux can read and write NTFS, performance will suffer, the disk will lack Linux filesystem features you might need, and Linux lacks any sort of NTFS repair tools. Thus my recommendation to switch from NTFS to a Linux-native filesystem. If Windows will remain on the computer, though, the last of these issues becomes much less important under Linux, and the first two issues favor NTFS under Windows. In a Linux/Windows multi-boot scenario, FAT is the most compatible filesystem; but it's got file-size limits that make it impractical for many purposes. NTFS is the second-best choice (or the best choice if FAT's file-size limits are a serious problem).