Select install, then chose the file you downloade from my site. After that look in the "layout" menu for the new layout you just installed. it's called "default"
If you dont see it try restarting XSI.
If you want to remove the layout afterwards go to View->taskbar.
Im not sure I got all the details right, and I cant look them up as I dont have XSI available right now. So if anything is unclear you can mail me.