adding users to DB

Hi,
I need to know how to add users to the wpDB users & usermeta tables. I am trying to write my own registration form because i need some fields in the db that obviously don’t exsist in wp default.

I am a fairly competent mysql and php coder and would really like to write it all in pure php/mysql without the confusing wp tags – presently i can’t even find the connection string to mysql. Two questions – are there:
[1]
Any clear step-by-step guide as to the many function calls in wp. Or
[2]
Any plugins that will allow me to create custom fields to the registration form for adding new users to wp

any help appreciated