Hi, for everyone of those who have trouble installing the Gd-Lib with PHP 4.2.3 and for all those who have an error when running php with gd-lib enabled i've got the solution:
Download the ZIP distribution (NOT the installer)
install it
enable gd-lib in php.ini
copy the gd-lib.dll in windows\system or windows\system32
it works, no more errors that php can't find or start gd !!
Sorry, if my post is outdated, i just wanted to help some people.
Have fun
zer0