This looks like a trivial issue but in fact it is not. Sony Vaio, in particular, will not let you disable the touchpad in BIOS or in Device Manager. Most instructions on the web will tell you to "Open Vaio Control Center, expand Mouse and Pointing Device, find checkbox that says Enable and uncheck it..." Well, guess what? It works only when laptop is fresh from the store with all factory default software installed. As soon as you made a clean install of Windows 7, all Vaio software is gone or stops working properly.
This instruction will tell you how to restore Sony Vaio software and bring this "Enable Pointing Device" checkbox back from abyss.
Step 1: Locate Factory Software for Your Sony Vaio Model
Locate your model number (mine is VGN-FW449J/B, I will use it for example since it is a very typical model) and go to Sony eSupport site.
The screenshot shows VGN-FW449J/B page, but you can easily change it by clicking on "change model" link.
Also, select your operation system from the list (see screenshot).