I vote for the Netmon (plug-in) approach, since it’s so easy to set up, and simply watch for the computer’s IP address to be ‘active’. (In my setup, I use WOLPlusPing instead, since I can use it to also ‘wake up’ my computer via Wake-On-Lan. Setting up WOL on most PC’s is straightforward but not always self-explanatory.)
Meanwhile, if you do go the more sophisticated route of having a utility program running on your Windows PC to negotiate other activities, may I recommend EventGhost? It’s free (although again, not entirely obvious how to configure!) and will allow Vera to send HTTP requests, which in turn can perform functions such as shutting down your PC.
If all you need is, “Computer ON? Do something.” then stick with Netmon and a virtual switch setup!