I've done a fair amount of work with the one wire interface, specifically the DS18S20 (the DS18B20's predecessor) in production environments. I tried long and hard to avoid having to run power to the device and just power them parasitically using current derived from the serial port, but in the end it just wasn't reliable enough and I added my own tiny power source. What I found was that the capacity to power parasitically was entirely dependent upon the computer to which the device was connected, which makes sense actually. For my environment (hundreds of deployed devices) I could just not take the risk.
If you're just trying to make this go for a one-off situation, then I'd say you have a 50/50 chance - either it will work reliably or it won't!
Let me know if I can be of any further assistance.