I found a 3.5mm cable lying around so I decided to experiment. I plugged one end in the earphone jack of my Windows XP laptop and the other end in mic jack the Windows 7 desktop. As expected, the sound played on my laptop were received as mic input. Then I got this bright idea of using XP Text-to-speech Sam to use as voice communication in TF2.
"Hello everyone on skial server. My name is Microsoft Sam"
People burst out LOLs and giggles.
MotleyHar: Hey Microsoft Sam, say my name.
MotleyHar: I love you.
Playing while typing was a challenge. So I played mostly Engineer so I can at least contribute while mic spamming.
"Spy around the base"
"Incoming Heavy Medic"
Since I'm typing on the other computer, I'm often caught with my pants down.
My laptop is running low on batteries so I think it's time to say goodbye.
"I'm leaving now guys. My batteries are running low."
Everyone bid farewell to Microsoft Sam.
"Don't forget to buy Microsoft Windows 8 on october 2012"
And everyone laughed their bottoms off.
THERAPIST: he sounds like that guy in the wheelchair, who was it again?
Microsoft Sam: you mean Stephen King
[some guy in the text chat]: It's Stephen Hawking.