Windows: Open your Web Crossing Configuration panel in your Programs listing. If running, then towards the bottom of the window it will say "Web Crossing: Installed and Running". If not, click "Start Web Crossing"
95/98: The server will also be present in your toolbar.
UNIX Flavors: ps -ef | grep webx
MAC: Look in the pull-down at the top-right corner, which shows a list of all the programs in memory.