At the moment there is only a (clumsy) work-around....

You should not enable the option "when the network directory is not available, keep trying". This will cause the task to stop as soon as the monitored computer goes down.
To make sure that the tasks starts up again when the monitored computer comes up, write a little .bat script (autostart.bat) containing these lines:
Code:

Start "task 1" "c:\program files\watchdirectory\wdrun.exe" -start TASK1
Start "task 2" "c:\program files\watchdirectory\wdrun.exe" -start TASK2
 

And use the windows scheduler to start this .bat file every 5 minutes. The commands inside it will start TASK1 and TASK2 only when they are not already running.

In the (near) future there will be a free add-on program available that will automatically do the above.

Gert