Differences between php3 and php4

Hi everyone.. I am new to php. I have PHP4.2.3 installed with Apache on my computer. I was practicing on the language from a book called "PHP essentials" by Julie C Meloni. I am facing many problems as many functions from php3 are not working anymore in PHP4! For example, header(), include(mydata.txt); and mail(). Also, to recieve variables from an HTML form, i had to add HTTP_POST_VARS("")!! how would I know that i have to add that?!. I have many similar problems due to the differences between the two version. I have 2 questions: 1. Is there any source (book or URL or whatever) that shows what have been changed between php3 and php4 and what are the new functions or values are? Something like a table or differences in functions. 2. How do u get the mail() and include() to work? Also, who do u get header() to header() function to work in PHP4?? This is the code i am using for the header() followed by the error message: ===========CODE============================ if (!isset($PHP_AUTH_USER)) { // If empty, send header causing dialog box to appear header('WWW-Authenticate: Basic realm="My_Private_Stuff"'); header('HTTP/1.0 401 Unauthorized'); echo 'Authorization Required.'; exit; } // If not empty, display values for variables else { echo " <P>You have entered this username: $PHP_AUTH_USER<br> You have entered this password: $PHP_AUTH_PW<br> The authorization type is: $PHP_AUTH_TYPE</p>"; } ===========ERROR==================== Warning: Cannot add header information - headers already sent by (output started at C:\Program Files\Apache Group\Apache2\htdocs\auth.php:9) in C:\Program Files\Apache Group\Apache2\htdocs\auth.php on line 17 Warning: Cannot add header information - headers already sent by (output started at C:\Program Files\Apache Group\Apache2\htdocs\auth.php:9) in C:\Program Files\Apache Group\Apache2\htdocs\auth.php on line 18 Authorization Required. Please help me here ... --------------------------------- Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, and more