Arduino and Twitter over USB cable

Hey I was looking to build a device that would lock my door whenever I send a tweet to a certain twitter account, and I would like the connection to the internet to be handled by the USB connection to the computer. I'd rather not have to get an Ethernet shield if not totally necessary. Any suggestions?

IF you can get a program then interprets serial comands and sends text to twitter, then sure :smiley:

It would mainly be a computer program thing...`

Mowcius