The difference is that the edition for $160 is an upgrader's edition. While you are still receiving the full Vista operating system, you are required to provide proof of ownership of a previous, qualifying version of Windows, and then install it on the computer with the previous version installed. It's Microsoft's way of showing its appreciation to returning customers, similar to other companies offering upgrader mail-in rebates. If you want to install Vista on a computer without a previous, qualifying version installed, however, you must purchase the full version.

Hope this helps,
John