aw98 - well i am assuming that means "a windows user 98" :-)
well, download the entire PHP version for the windows os. extract it to lets say c:\php, and now in the "extensions" directory or c:\php\extensions there should be a file "php_gd.dll" - place this file in ur windows directory, try it in c:\windows\ , system, system32 or whatever, not sure of windows 98.
place a phpinfo() in some file and check to see if u have gd support.
cheers
nilesh