That's the thing, you should have selected install beside windows.
Anyway, don't need to go through all these again.
Just delete your D partition (Not from windows), on the screen which you are on right now (On Ubuntu)
Now create 3 partitions there...
1. / (root)
2. /home
3. swap
Make swap 1GB
Make / (root) ext4 and of around 30GB.
Make /home as ext4 and use the remaining space
NOTE : I stated this guessing your partition is of around 97GB (As you stated above)
You can allocate space according to your needs too.
For that I'm explaining the things below...
Swap is like virtual memory in windows. So peoples here have diff. opinions about how much space should they allocate for swap. It depends upon RAM and all. So if you have > 1GB RAM, 1GB Swap would suffice (Personal Opinion, Other people can suggest much space)
/ (Root) is the C drive of Linux. So allocate space according to how many programs(read applications) you'll install. In general around 30GB is more than enough for a Home user like us.
/home is the My Documents of Linux. Your personal files / folders / preferences config files and all gets stored here. This is optional partition. In general if you don't create this partition it'll be created under / (root) allocated partition.
But I'd recommend creating /home as if you format / upgrade your OS later, you won't loose your files. See, it's like D, E and other drive in Windows, you don't loose data while formatting the Windows in C...!!
Hope it helps