Sandboxing apps to protect your Windows computer
Similar to Sandboxie, Bufferzone is more about isolating threats from the internet than completely locking down your system. It's designed to isolate apps like your web browser, email, and peer-to-peer programs. Downloaded files inherit Bufferzone's protection, so if you install something that was downloaded from a protected app, it becomes protected as well.
BufferZone is free to try for 30 days. After that, it's $39.95 to register for home use. Trustware also offers various enterprise-grade solutions. Vista users can sign up for a beta version tryout.