This can be done in two minutes.
Load up Solar Jetman.
On the main menu, select 'Continue' by pressing
and then press
.
Input the following code:
ZQBPQQQQDMNB and then press
. Do NOT press
or it will ignore the code.
You will start with 99,999 points. All you need to is fly around on the first level and shoot one of the pellet-firing 'turrets' on the rocky walls, which are worth 5 points, and you'll get the achievement, because you will have 'earned' 100,004 points.