can i run houdini on a windows computer without actually running the installer? Is it possible/will it work to just copy the installation folder to another computer and run it on the 2nd computer?

No, you cannot. One important thing the installer does is install the HoudiniServer service. Without this, Houdini is unable to check out a license. For more explanation of what HoudiniServer (also called hserver) does, see www.sidefx.com/faq/license-management/#faq6. In addition, depending on what type of license you have, you may need to install the license server and licenses.