Have you searched this forum? There are already many fine answers to this question. I'm not so enamored of "best answers" that I don't want people to just read the old posts.
With that off my chest: You need to do the install onto a new SSD, or allow the install to reformat the SSD, with no other drives plugged into the system. If you had a bootable drive plugged in when you installed Win7 to the SSD, the boot process will actually start from that bootable drive. Some very good forum denizens state that if you install with two new drives in the system, it will create a 100 MB partition on the drive that you are NOT installing to and boot from that.
So the trick is to ensure that the master boot record and boot loader are on that SSD, which is best accomplished by having only that drive attached when you do the install.
After that basic, you will find a lot of good guides on this floating around. The most important points are to
1) Set the motherboard controllers to AHCI mode before doing the install.
2) Have the SSD be the only drive on the system when you do the install.
3) You can change the My Documents and My Everything Else folders to point to the HDD.
4) There are dozens of tips on optimizing the OS for SSD use.
And, if you have a huge game to install, there is a way to install it to the HDD even if its installation procedure doesn't prompt for an installation location. This requires a simple registry edit.