I am not sure how you installed Apache and PHP5 since there are numerous ways. In my instance, Apache comes with an uninstaller that can be accessed from "Add/Remove" programs, and PHP is manually installed by creating the directory C:\php and inserting the unpacked files there. php.ini is copied to the WINNT folder. So for my case all I would have to do is uninstall apache via add/remove programs. delete the contents of the C:\php folder, and delete the php.ini file.
Hope this helps
There is no such thing as a stupid question, unless you ask it more than once :)