OK,
you can play almost any character as evil except of course a paladin (unless you use SK) but some classes, like Assassin cannot be good.
Neutral and esp. good characters will be angry if your reputation drops too low, so create a party with mostly evil and neutral chars.
My ideal party would consist of:
Korgan evil berserker
Viconia evil cleric
Edwin evil mage
Jan neutral illusionist/thief
Jaheira neutral druid/fighter
I would advise you to play realistically: don't run around killing everybody in sight and giving stupid answers, that's not evil, that's plain stupid!
Evil guys need to make money too, so instead of turning down quests you should accept them. Where a good char might accept a quest to help people, you'd do it just for the money. Apart from that, playing evil can be fun, especially because the evil NPC are so good. Enjoy!
------------------
Melusine
Your voice is ambrosia