Well, usually, there is not »installing« for downloaded nightlies for windows. you can, however, backup the old 1.0 version (I for one, recommend that strongly!), and then replace the old folder with the new one. So just rename the old folder to Foldername + »old« or something, name the decompressed folder from the nightly into the original name of the old folder and place it where the old folder was before.