Max threads using asynchronous invocation

Hi,

I use an asynchronous call to execute a method in a
windows service :

TargetSystemDelegate TargetSystemdelegate = new
TargetSystemDelegate(TargetSystem .Invoke );
AsyncCallback cb = new AsyncCallback(TargetSytemCallback );
IAsyncResult ar = TargetSystemdelegate .BeginInvoke(ref
activity , cb, null);
Is there a limit about how many threads could be created
by the windows service ?
(Like in ASP.NET using maxWorkerThreads attribute in the
processModel element in machine.config)

If not, should I explicitly use the
System.threading.ThreadPool class to ensure a maximum
worker threads ?

Other question : How can I retrieve the input parameters
of my call in my callback ?
(for the moment, I use REF parameters)
Thanks,

Arnaud