Turanil said:
Now the second point:How to integrate / explain some magic (ala Cthulhu) in a sci-fi game, so it doesn't look totally weird, kitsh, or what not? Ideas?
Well, actually there is no 'magic' in the core Mythos stories; it's all just science so alien that human minds are incapable of understanding it, and they have to distance themselves from it to keep from going totally nuts (thus the incantations, the material componants, and such; all that is window dressing to put what is happening into terms a human mind is capable of understanding).
Many science-fiction writers have novels and stories about 'magic' grounded in science. The Lord Darcey series is probably the most famous; it uses several laws of magic (Law of Similarity, Law of Contagion, etc) .
That, in itself, is one way: 'Magic' in an SF game can be science so complex and capable of so much that there is no effective difference between it and magic. Kind of like a Star Trek replicator. In GURPS 3rd ed, once you get to the super-science levels (about TL 16+?) the entries for 'War' and 'Medicine' just say 'Poof, you're dead!/healed!'.
This especially works in the classic Star Trek original series where a group of people lose their knowledge of technology and regress, but still have their scientific wonder machines from a previous era. The machines still work, but the people accept what they do as miracles.
Psionics is another way of going about it. Psionics generally involves purely mental control of your surroundings, generally through some form of energy control (which gets you matter control; they're the same thing after all). A very powerful telekinetic is going to be almost indistinquishable from a magician: they could control the weather, kill people with lightning, change lead to gold, teleport by ripping open wormholes, manipulation of the Higgs field to fly or otherwise counter gravity, etc. Make them powerful enough, though, and you practically go into superhero levels of power. Thing Ironheart from Babylon 5; he was manipulating atomic structures, basic energy forms, etc.
Another way of going about this placing someone in contact with the first few fematoseconds of the Big Bang, or a singularity (controlling the singularity is your problem); the laws of physics had not completely formed yet, so really anything is possible to them. They can go faster than light, make heat go to hotter regions rather than colder ones, etc etc. Manipulating quantum field effects like this places you firmly in the realm of super powers; look at the Wild Cards series for a Sci-Fi take on supers.
The only thing you have to do, like in any other genre, is establish your ground rules and never break them.