"However, I don't even have a windows OS on my computer, only Linux. So how can I move the /windows/D and /windows/C space over to / (which I think is Linux's space on the harddrive)?"
I would just leave three partitions on your hard drive and use the space for something other than Windows. To do this:
edit /etc/fstab and comment out the lines for /windows/D and /windows/C by putting a # in the first column of the lines. Make a mental note of what the partition addresses are (for example's sake I will assume /dev/hda1 and /dev/hda2). Then either:
Now you can format the two partitions, for example:
If you don't understand then see:
Then you can use the two partitions for whatever you want. For example you could place /home on /dev/hda1 and keep backups on /dev/hda2.
Be prepared. Create a LifeBoat CD.