Invincibility cheat!

On the video mode selection screen, press "F7" instead of "Enter".
Then at the game press "i" at any time to activate invincibility!
(try again if at first you don't suceed but be careful, pressing "i" 
again will deactivate the cheat!)

Hex cheat:

If you want to shop at no cost in the shop, you have to overwrite the file XENON2.EXE bytes 1C602H to 1C631 with 00.