So I got the latest Occidentalis distro from the fantastic Adafruit Industries who built in a few handy utils and libraries (like SSH and libs to enable access to the GPIO pins). After a few test runs from the floor in front of the TV, I hooked the Pi up to my router with an ethernet cable and powered it up. Using SSH on my Linux netbook is straightforward, but you need extra software for Windows - PuTTY works well enough (although the connection has to be reset occasionally - not sure if this is the router, Pi or PuTTY...)
Next I got hold of my BMP085 pressure/temperature sensor breakout board, which uses the I2C bus to communicate with other devices. The Pi has built in I2C support brought out on the GPIO pins (one data and one clock pin for each I2C bus). Again, Adafruit have made a library and set of example programmes for interfacing with the BMP085 (amongst other things!). Connection to the GPIO pins at the mo is through an old IDE cable and hook-up wire. The Pi has 3.3V and 5V outputs right next to each other - so be careful connecting up 3.3V devices! Eventually I will make a breakout board, or buy one...
Currently I'm attempting to use Cosm to publish this data, but the examples in Python are defeating me at the moment.