Like most religious ideas, it's all symantics - god (small 'g') is just the idea of an omnipotent being with an untold power over some aspect of our little chunk of the universe. Sometimes, there are lots of them, sometimes it's just the one. God (big 'G') is the dude in charge of the Christian bit. It's just an example of the limited scope of the English language that the same word describes both the idea and one particular implementation of it.
Satan is an idea that just happens to be present is all the Abrahamic faiths as the opposer of God (or whatever His name is), it just means "the adversary" or whatever. So it's pretty clear even from the name that to have a satan, you need a god. You can't be an opposer without someone to oppose.
The idea of him being some big red guy that bleeds evil is just one messy interpretation of the original idea though - Lucifer was the head Angel, he questioned God, God got a bit shirty and insecure about his cock size, and threw Lucifer out of Heaven. As such, Lucifer become God's adversary, hence the name change. His role wasn't to be evil himself, it was to tell people they don't have to follow God's word (thus giving them the choice of being evil if they so wish). So for the most part, the whole idea of Satanism is a bit rubbish; it's an entire religion based around the idea of not following a set of rules - which is essentially what religion is, thus making the entire concept completely obsolete and paradoxical.
The problem is even people who claim to be atheist still see god and the devil as good and bad, which they aren't - they're just opposing ideas. One gives you a set of rules to live by, one tells you that by living you'll set the rules.
The 'Satanism' that people like this Dissection dude follow is nothing to do with actual Satanism. You know how you tell some little kid not to do something, so they do? It's pretty much the same thing - this kind of Big Nasty Evil Satan following only ever happens where Christianity is rife, simply because it's following the God-fearing Christian blueprint of the Devil. It's just a neat way to rebel against the ideas you've been brought up with. No one from a neutral upbringing ever goes "Gee, hating everyone, killing small animals and digging up graves sounds like a wizard basis for belief system!".
However, LaVey Satanism isn't remotely to do with the Big Red Guy, it's simply about the idea preservation and advancement of the self (known as the left-hand path, hence the Entombed album). LaVey made it perfectly clear that he did not believe in devine beings. The irony is that he preached about self advancement and not following other people's rules - in the process getting thousands of people to... er... follow his rules... and pay him for the privilege... thus making himself lots of money, or advancing him if you will. Regardless of what you think about his pseudo-philosophical religious bullshit, the guy was a marketing genius and his legacy of making people look like stupid, ignorant, selfish pricks is almost unsurpassed.
Steve
