This is probably possible without Parallels. You need to configure growl to accept messages from across the network, google for this.
Then, on the windows side, you'd need to do scripting for the various messages you want to send. Installing perl would be easiest, I think, there is a Growl module. It might be possible from a cmd.exe bat script though. Check into it. Assuming the apps you want to do this from even have the hooks.
On linux, this would be easy. But windows isn't even really an OS. I guess you know that though, since you have a real computer.