first, thanks for your answer and effort.
Well don't get me wrong, but it's not like I'm a beginner with either computers or Linux. :-)
The fancy thing about the shortcut-handling I've written for Windows is that to, for example, activate Firefox, I just have to press Ctrl+Alt+F and it will use an already open window if there is one. Same goes for all other shortcuts I've defined. Cycling through Alt+Tab is a major pain and not nearly as effective as just pressing the shortcut of the application I want to jump to.
I've just been told about the program wmctrl which I can use to accomplish this. I'll post a new message when I've finished a solution for this.