Probably the same thing I did. I got my laptop about the time eCS1.2RM came out. I just put eCS RC4 on it. I didn't install XWLAN, eCS did.
You don't really work with eCenter. I assume eCenter has a clock at the right end. Right click on the line at the end of the clock. That should get a box that includes Create new widget, and that should have XWireless LAN Monitor.