HowTo : Android ICS Tethering & sending SMS from desktop
The nice thing about Android is that there are many geeky Apps available. Some of them are even open source and free. So there are many different Apps for your task. Here are the ones I am aware of:

Android Remote Notifier

Project Page - Play Store
Forwards and send text messages via bluetooth

GTalkSMS

Project Page Forward and send text messages via XMPP

Other

Can be found in the related questions on Android Enthusiasts:


How do I send SMS from PC through Android Phone or to Android Phone?
How can I be informed through my computer if a new SMS is received?