The window size will be altered by the horizontal and vertical amounts specified in the two parameters. The left and top edges will stay in the same place but the right and bottom edges will be adjusted to the new positions.
There are some security implications for resizing windows in Netscape 4. This is to prevent you hiding a window by making it too small.
Your script will need to be granted the UniversalBrowserWrite privilege to allow it to set the window size to less than 100x100 pixels.