Another question is coming, how could I put the rdesktop icon on the desktop with paramater pre-set?
Do you want the icon added to the icon bar (wbar) or directly on the desktop?
If you want it on wbar, you need to get three lines into ~/.wbar, one to specify the icon, one to specify the title and one to specify the command line to be executed. You can snarf an icon image from some other extension or make your own - the rdesktop extension doesn't include one.
.wbar is a text file so you can just edit it with your favorite text editor for testing, then create an extension (or pseudo-extension) to make the entries automatically.
Search the forum for topics relating to "wbar".
If you want the icon directly on the desktop, I seem to recall there was discussion of that on the forum as well, though I don't remember anything about it that would make a good search term.