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PC parallel ports vary greatly in their current capability. You can't rely on being able to draw more than about 10mA in total.
A few laptop ports give out closer to 4V than 5V.
Drawing more than microamps from a parallel port is likely to slow down the rise time when an output goes from 0 to 1. I would not count on being able to use the port for high speed data.
If all the output lines happen to be zero for a while then you are going to loose power.
The only real option is diodes from all of the output lines to a capacitor and a low drop regulator of some kind, perhaps a resistor and a zener diode.
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