When I did my hard drive install, I too used my Windows D drive to both hold backup data from the Windows C drive and profile room for Linux. In my case, I partitioned the drive first, but after doing the install, it seems I didn't need to. When you follow the hard drive install menu, you'll see that partitioning the drive is one of the steps. I too was nervous about doing this so I made sure I had a backup of the data on my D drive before I started.

You might want to play a bit with the QTPARTED utility to get the feel of how it works. You can do this without committing the changes. You'll find you have to shuffle things around a bit by first reducing the size of the original Windows partition which leaves you some free space. Once this is there, you can create the new partitions for the Linux install and another for the swap file. I found the install to be pretty much painless when I got to it.

Having gone the permanent install route, I"m glad I did. It opens a number of door in Linux for you, such as providing a true multi-user environment and the ability to add, update or remove applications in your setup. Good luck and I hope this helps.

David