To respond to the OP, there's a link to a good depiction of a good Evil campaign in my sig, in comic format. Some good guidelines for an Evil campaign are:
Make sure that they have lots of reasons to stick together as a party - D&D is a party-based game. If the players are constantly screwing each over or outright murdering each other, the dynamic will quickly break down, which usually isn't any fun - especially when players start designing replacement characters with the sole purpose of screwing other players over. There are several ways you can solve this:
Give them an Evil Overlord who will be very displeased if they screw around - obviously you should permit them a fair bit of freedom in how they do stuff, but if someone's messing up the party dynamic by stealing from the other party members or not pulling their weight, they should be reprimanded by The Overlord and annihilated by him if they continue to fail. Obviously this should be mainly used as a threat - don't get too involved in the party as a DM, and definitely don't punish anyone for screwing up when it isn't their fault.
Put the bad guys on the back foot - Orders of paladins, questing angels, inquisitors, dragons and unicorns are all good foes for an evil campaign. They're powerful, hate evil, often have good ways of detecting and rooting it out, and should be used to make your party feel as though all they have in the world that they can rely on is their friends in the party. Make them feel hounded as they try and accomplish their goals. Make sure they realise that if they don't stick together they're going to end up purged.
Make sure any quests you give the party have obvious gain for them in it - Good parties are often willing to go on quests for the goal of helping the local populace, or won't ask about rewards before they do something, and will take whatever's offered. Your evil party won't. They'll want a bunch of cash, and they'll want half up front, and may not even do the quest once they get that half. Make sure you've thought about all your rewards in detail before you set any quests.
Find out what the characters want to be in 10/20/30 levels time, and work that into the plot - Most evil characters will have archetypes like "Demon Lord" and "Spymaster" and "Assassin". Make sure they're able to work towards their goals, like leading an army of demons, or having a web of spies/assassins throughout the land.
