First of all you need Apache Server, PHP, MySQL and a Forum Script i.e. phpBB or Invision or vBulletin.

Download phpDev here

http://keihanna.dl.sourceforge.net/sourceforge/phpdev5/phpdev423.exe
and you get a bundle of all the things above.

exttract & install php dev. start the apache server,its 90% done.

upload the forum script to X:/phpdev/www/public
(x is your drive, usually C: )

now to access the forum through internet you will not know your IP address thru ipconfig command..

go to

http://www.whatismyip.com

see whats your IP address.

now go to

http://your ip address/public/your forum directory/install.php

thats it!