There's a great howto on the green board for converting your keg.
As far as spigot and weldless fittings. Get a zymico weld-b-gone ... and a half inch stainless ball valve and a barbed nipple size of your choice (in stainless).
As far as what you do inside the keg. I did a zymico bazooka t screen and their copper adaptor with an elbow.
you can buy weld-b-gones at northernbrewer and morebeer i believe. they even come in kits with everything you need spigot side anyway.