The atmega8 io pins have a maximum rating of 40mA per pin... But I'm not seeing maximum power consumption for the converter while converting in parasite mode. I did see the voltage drop about half after the start conversion command, so it must be trying to do parasite power.
Enabling pull-up on the data line by the microcontroller didn't seem to fix the problem. Also, I didn't spend too much time on the oscilliscope trying to perfect timings in accordance with the microcontroller.
So the fet is required to supply the device, and in that case, I assume a second digital out could be used to control that pull-up. If it could be done with the USB's 500mA, what would be suitable for this application? I need to order a few, there are no FET shops around these parts.
With a 750ms delay on conversions, if you had numerous devices on a line, it wouldn't be a very quick operation, to say the least. When I saw one when ordering my arduino, I thought it might be an interesting thing to use, but thermistors are just so much cheaper! 