In addition to Madman's post:
The SSD is intended to contain your operating system. When you install a program, install to the SATA drive. Note that this does not mean that all the installed files required for the program to run are on the SATA; in actuality, most programs insist on installing files to the C:\ partition which is on your SSD. This is good, because your programs will load and run much faster if on the same main partition as your OS. However, you will save a lot of space if you instruct your programs to save data to the SATA drive.
For example: you are a graphic artist and you are working on a project. Everyone knows that music and graphics (including video work) take large amounts of storage. So, when saving your files, you initially save a new project to the SATA. Now, every time you save as you go, it will save to the SATA instead of the SSD. That saves huge amounts of space on your SSD.
Actually, the difference in price between a 250gig SSD and a 500gig is pennies, realistically. Right now Amazon & Newegg have 500gig SSDs for around $130, and a 250 is only a few bucks less. False economy to go small.