As Ben mentioned, this is not the best group for answering this question.
The official Windows term for this is "autologon" and Googling for this
term yields many hits, the first of which is:
http://www.windowsitpro.com/Windows/Article/ArticleID/22731/22731.html
Be aware that you should be super careful in the Registry Editor. There is
no "Undo" feature nor any confirmation of any changes/deletions. If you
change or delete something you shouldn't, your programs may not run and/or
Windows may not start. Messing with the Registry will also cause you to
burn your toast, and small ferrets may accost you on the street with no
provocation. You've been warned.