the easy way is to take out any drive that is not the one you are working on and partition it as you see fit. Return other drives when done.
The not so easy, but still do able way is to leave the other drives in, partition the new drive using Gparted or the like, and be sure to label your partitions. That little extra 3 seconds of typing can save loads of confusion on the install process.
Then you can install as you see fit. then once you go into the first boot after driver install, go to disk management and manually assign drive letters. That will allow you to set the drive letters as you see fit.