I can't imagine what could take up 100GB of space, except video. :eek: I would remove everything non-essential, then partition the drive and store the image on the new partition, You can then just leave that partition and image in place.
If that's not feasable, then partition the new drive, store the image on the second partition and install Windows on the 1st partition.
But I agree that making an image of 100GB is not a great solution, although it would compress to around 50-60GB with max compression. You're not likely to gain much in performance with the new drive, so you also have the option of using it as your storage drive for the time being. Copy what you need to it then wipe the old one and re-install Windows to the same drive.
Still another option is to do a disc cloning operation to the new drive, re-sizing the current volume to the new drive's size. The drive will come with a tool for doing this. Then you can wipe the old drive and copy what you need from the new drive to the old one before wiping the new one and re-installing. Kind of a round-about method, but reasonably safe.
In any case, be sure you are fully backed up before attempting any of this. If you need to use the new drive to make an image of the old one, that's the safest way to go. Just be sure you are not formatting the new drive when you install Windows, cause that'll erase the image. Hense the suggestion to partition the new drive first and store the image on the second partition. Hope this helps.