The Virtual Roman House has been changed from a version that required the Unity Web Player plug-in to a new version using WebGL. The new WebGL version has the advantage that it should work on any machine using a recent web browser, without requiring a plug-in. It does have some disadvantages though (at least in its current state). For one thing, the file size is HUGE (14 MB). If you find that the WebGL version does not work well for you, and that you preferred the previous Web Player version, you can find that version here: http://www.medievalist.net/unityworlds/oldromanhouse.htm (though it may no longer work).
The new WebGL version employs a different system of navigation. You can look around just by moving the mouse. To walk around, you must use the W, A, S, and D keys. Note that S and D will move you side to side (strafing). To turn, you need to use the mouse. Once you click a key, your cursor will disappear. To get it back, just hit the "Escape" key. This behavior is a WebGL issue.
Enter the WebGL Virtual Roman House