TestComplete can do load testing for applications which use HTTP/HTTPS and SOAP protocols.
I am not experienced with Silverlight applications, however a quick search on the internet shows that
Silverlight uses RTSP protocol, but
it can be changed to HTTP.
If this is true, then you can start with reading about Load Testing in the TestComplete help (topic "Load Testing of Web Servers With TestComplete - Overview").
But I'd like to hear Support opinion as well (regarding load testing of Silverlight, Flash and Flex applications) :)
