To save me doing it myself (i'm not sure where to start, 40k is such a big setting). Are there any really good online sources that serve to explain not only the setting, but the way it should work (eg, that technology is arcane, feared and lost). I want to explain the setting so that the 2 players I have 'get it'. Thanks.

Also how can I know what level to design suitable enemies for them: currently 2 rank 1 characters (psyker and assassin) without them being overwhelmed or given too easy a time of it)?.

I would just search on the 40k wiki or go to a game store and read a few codexs for warhammer 40k, they may be a little in depth but thats how the universe is, as for enemies, have them fight the scum of the earth for a while, mutants with improvised weapons, scum with only a pistol, then have a few of them, say 3, and your characters are going to have a few problems, but still be able to win.

The Imperial Primer

I also have this in a great, illustrated 22-pages long pdf. If you need it, hit me with your e-mai address and I'll send it over.

I can't see any PM function here.

Never mind, I uploaded it to Scribd.

Here's the link: http://www.scribd.com/doc/74538140/Imperial-Primer

Impressive, thanks.

Why not upload it to Dark Reign?

Oh yes, please put it at darkReign. Because with Scrib it, you have to give them all the rights to do every thing with your facebook account. And I hate this.

Cheers