the URL are case sensitive and don't error if you make a mistake, i think the bigger problem is that the ActiveX mode fails all the time.
I would love to hear about any other blogs with other plugins, the current one hasn't been updated since 2007!
rdp://targetcomputer/?geometry=1024x768&bpp=16
Note that 1024x768&bpp=16 will look small if you have a very high res system ,so you might have to go bigger.