If you can't find installed application from the menu, it's not there

Crawl doesn't have menu entry, because it's basically impossible to make it work with default osso-xterm without manual adjustments. So start X Terminal and type crawl to start it. You probably have to change to smaller font.

I don't know why rdesktop doesn't have a menu entry.

Some programs are actually desktop or toolbar plugins and they are not found from the menu.