good question.
the max one device can draw from a usb 2.0 is 150milliamp hours,
so take the battery milliamp hour value, divide it by the number of hours normal operation to get the milliamp hour consumption of the nc10, then add 150 mAH to that figure to get the total consumption of the nc10 AND the dvd drive together, then tack your initial battery value again and divide it by this new total value to get the number of hours you will be able to run both together (which is the case during dvd playback).
it’s gonna take a fair ammount of juice. it could cut your run time by as much as a third. maybe more. of course, that is using the peak consumption values of the drive, so in reality it will probably draw a lot less on average.