Go to the WotC D&D site. Go to the archives section. Use your browsers find command and search for "conversion" They have a pdf conversion guide.
It does not cover half ogres and swan maidens so you will have to make up rules for them and give them ECL xp modifiers depending on how much better than normal races you make them (compare the half ogre to the half orc).
The witch doctor is most likely either an adept, a shaman from any of the supplements (Mongoose's shamans, Green Ronin's shaman, OA or World of Diomin shaman, Netbook of planes shaman, etc.) or a druid or cleric with appropriate domains, or multiclass cleric wizard or sorcerer. Lots of flexibility there.
The pdf conversion documents suggests making special kit abilities into feats. Everything else should be pretty easy (but expect high sterngth 2e characters to be really high strength 3e characters).