automatic login..

hi, I created one site , and i implemented the concept of mypage same like as google or yahoo or excite.com, now my problem is i just want to put a line{href} in my mypge as set as home page so when the user will click on that , so it will set this page as default page.. And next time he/she will come then no need of login the mypage will open automatically, I think i hv to track the cookies and store the ip into the table or something like that,,,,, plz any body can help me and gv some hint , for how it is possible... any logic or ideas, thnx.. Open Source Ki Jai.. ~ ganu maharaj..