On CPU start-up cause Start-up my Device Connected on ParallelPort?
The simplest way would be to look at two parallel port pins and use a small amount of logic.

If you look at both pins 2 and 3, for example you can do the following:


If both pin 2 and 3 are off, the device should be off.
If pin 2 is on but pin 3 is off, the device should be on.
If both pin 2 and 3 are on, the device should be off


This is called "Exclusive Or" or XOR  and the truth table is as follows:

A   B   OUT
0   0   0
0   1   1
1   0   1
1   1   0


There are many ways of implementing this in hardware - the simplest is probably to use the 74xx86 (eg 74ls86 or 74hc86) logic chip.  This contains 4 XOR gates which each has 2 inputs to it (you can get other input quantities, and chip densities).

For example:



Which could be turned into a circuit as such: