I put this guide on the Lenovo forums. I just remembered that I posted here as well, so I'll update this for anyone else who happens to come along. This is the solution I found:
Installing Windows 8 onto a Crucial SSD inside a Lenovo Y400
WARNING:
This is a very tricky and frustrating process if you do not do it properly. I am posting here because this is a top google search, and I could not find any other adequate information elsewhere during my own struggle.
Things you need to understand:
The Lenovo Y400 is going to come pre-installed with around 100GB of bloatware. The bloatware is installed in your default Windows 8 installation, and backups of the bloatware exist in separate partitions. All this bloatware makes it impossible to have a simple transfer of data onto a SSD less than 256GB in size. Deleting it is time consuming, but once you delete it all, you can make an image of your OS and never have to deal with it again.
Something else:
You do not own a copy of Windows 8. This makes reinstalling Windows onto a new drive rather tricky. You will not have the normal options of creating a partition table when you boot up from your self-made disc.
I am not going to provide detailed steps, but general guidelines for you to figure out on your own. This is a time consuming process, and I do not advise it for anyone without patience or knowledge of computers.
Let's begin:
You must create a Bootable Repair Disk along with a System Image. A DVD is easiest for the boot disk, USB drives are possible. A large thumb drive or external hard drive is easiest for the system image. I highly advise against creating a series of disks for your system image. The Repair Disk is independent of the files on your hard drive. The system image is a copy of everything you have. Create this before doing anything that will risk compromising your laptop. They will reinstall everything from scratch. To create them, start up Windows 8, press Windows Key + C and search for "Windows 7 File Recovery." Your options are in there. Yes, Windows 7 is not a type-o. This was a pain to find.
Windows 8 will refuse to install on your SSD drive through normal means. Other guides that advise removing your HDD before trying to install on your SSD did not work for me. It will give errors complaining about locked drives or missing partitions. If you attempt to partition your SSD manually, and then make a mistake, your laptop will refuse to boot until the SSD is removed. The SSD is not broken, and can be cleaned if plugged into another computer. I did this, and fixed it by purchasing an adapter off amazon ($5) that allows you to plug the mSATA SSD into an ordinary SATA desktop.
The only option I found that would work is the Disk Clone option in EaseUS Todo Backup. There is a free trial for this program available from their website. Before cloning, you must delete and resize your large 1TB HDD down to a size less than your SSD. This includes all those bloatware partitions. There are only two partitions that are required: The main Windows8_OS partition and the SYSTEM_DRV (EFI System Partition) partition. Important clarification: The large 1TB hard drive must have paritions with a cumulative value less than your SSD. The rest of your large HDD must be unpartitioned space.
Good luck! It's worth it in the end. Hopefully you wont make as many mistakes as I did.
EDIT: Going to add some more bits of information:
* Do not bother calling technical support for either Lenovo or Microsoft. You will be told to contact whoever you didn't call, be transferred back and forth to "advanced technical help," told you need to purchase a retail version of Windows 8, and other useless things.
* Be very careful opening your Lenovo Y400 for the first time. It sticks shut and you can break the casing or bend parts inside the computer. After the first time you take it apart, it opens rather easily.
* There's a guide floating around out there for the Y500. It's not actually for the Y500. It's for a Y580 or something, the older Lenovo model. It did not help me. If you decide to follow it, be aware of the model number. It wont hurt anything, but it will waste your time.
* On an unrelated note, I highly advise you install the program Core Temp. It's a freeware program that shows your CPU temperature. As with all gaming laptops, they run very hot when playing newer games. A temperature above 72 C will shorten the life of your laptop. The Lenovo Y400 will run newer games on high setting with dynamic shadows, but it will also go up to 90 C.