There is a way to disable balloon tips in the registry, or even create your own, but as your needs are specific to network connections, display these and disable them by right clicking the relevent icons.
Every time I open the lid of my laptop and it comes out of standby, I get balloons that tell me 1) That the ethernet port is "unplugged" and 2) That a wireless network connection has been found.
I'm sitting right next to the wireless access point, I -know- it's connected! Also I don't even own an ethernet cable. So how do I turn these messages off?