How can I make Windows 7 as small as possible?

I keep getting downvotes on this question.

I'm very interested in answering questions, and not just to hear myself type, but because I want you to be successful. Please, instead of just downvoting, give a reason and I'll do my best to remedy the situation.

So here's my answer as it currently stands:
There aren't a lot of ways to shrink 7. The largest part of the OS, the WinSXS directory, really can't be modified unless you really really have a hankering for pain and misery. You can use "Turn Windows Features On Of Off" in the Programs and Features dialog to disable and remove any unnecessary bits, but the source files will still be there in WinSXS.

So, you're left with paring down the other stuff. Removing any and all unnecessary apps, user accounts, directories, turning off Hibernation, shrinking the pagefile, uninstalling programs, emptying temp directories.

If you are willing to make it all go away though, I'd just create an image of the Windows 7 install and save it on the 1.5TB drive. Then if you ever need to come back to 7 you can simply restore that image and be right back where you left off.

UPDATE: imaging discussion

To put it simply, no.

Imaging is ONLY a choice just before deciding to wipe Windows 7, which you say is a possibility in your original question.

Once you create the image, you cannot use the system inside the image until you "reimage" that image to a disk (you can put it in a virtual system, but that's another discussion).

Just as you cannot work on the files inside a ZIP archive without extracting them because the ZIP archive is meant to be a storage package, not a "use" package, you cannot use the system inside the image until you "extract" it back.

The image is ONLY to make the transition BACK to Windows 7 easier. It is NOT to allow you to run both Windows 7 and 8 side-by-side.

Here's your situation: You have a small primary HDD and there's no way you'll get both Windows 7 and Windows 8 running on it. No matter how small you shrink 7, it just won't work. So, then your only real option is to clear Windows 7 off the SSD and then install Windows 8. But that will make it difficult to get back to Windows 7 if/when that is necessary.

Creating an image of Windows 7 only makes the transfer BACK to 7 easy as you won't need to reinstall everything and get everything set up again.

You can also use a utility like RT7Lite to reduce the actual installation size of Windows. This is accomplished by removing unnecessary components and features from the operating system, and removing them from the installation itself.

Depending on what you want/need to remove, you can drastically reduce the size of the installed operating system. It also allows you to slip-stream Windows updates, hotfixes, drivers, and service packs pre-installation.

I shrank the 64-bit version of Windows 7 SP1 (size of the actual .ISO file) from 3.09 GB to 1.64 GB.

You can create a ripped version of win7 very easily with the tool called RT Se7en Lite it allows you to remove a lot features from windows, which you might not need, after that you can reinstall it. Anyway you have to look and tune a bit to get the maximum out of it.