The original software (Windows and Programs) are kept on a special recovery partition on your disk. If you only formatted the C: drive, then this information should still exist.
To restore the system to it's original "out-of-the-box" condition, you need to perform some preliminary steps and when you restart the computer, press the F10 key while the Sony logo is displayed to access the System Recovery menu.
Here are detailed instructions from the Sony web site:
If for some reason, your recovery partition has been deleted or is not functioning, you will need a set of recovery CDs.
Ordering/Pricing Information can be found at the Sony Parts and Accessories web site. These CDs are usually pretty inexpensive as they are simply replacing software that you already have a license for (built into the price of the computer).
Here's a link to the Parts and Accessories web site:
If your system is an older model, the CDs may no longer be available at the web site. In this case don't panic just yet. You can call Sony (see above web site for numbers) to see if they have the CDs available for purchase.