Yes, my installation was later on successful. It's long time now, can't exactly remember how was it done ?
Mine was slightly different situation in the sense that my PC win 98 already had PHP 3.
I upgraded to PHP 4. And since some trace of PHP 3 were still remaining, my Apache was still detecting PHP 3.
After having changed the httpd.conf, keeping the php.ini in Windows directory (remove the old one, php3 etc. if any),
restart the machine, restart Apache, remove cache from browser and run a script with phpinfo(), it should work.
Make all the necessary changes in httpd.conf for the PHP, like php handler and script alias, etc.
If Apache is running while u are making all this changes, 1st shutdown apache. If it fails to shutdown, kill all processes of Apache (CTRL-ALT-DELETE), whereever u find. There may be > 1 apache process in the dialog box.
Try all this. it should work.