I added some pictures so it'll be easier to understand.
In this guide, we will be using Microsoft Visual C++ 2008 Express Edition and TortoiseSVN.
1) Download OpenAscent source code (SVN -> svn://openascent.com/openascent/trunk/) Username: anonymous, leave password field blank
2) Download warper source code Filebeam - Free Fast File Hosting (Thanks to Wareagle920 for link)
3) Rename the TeleporterItem.cpp to Warper.cpp and move it to \trunk\src\scripts\src\GossipScripts
4) Add Warper to setup.cpp, setup.h and makefile. (Just see how the other names are there)
5) Go to projects folder and find GossipScripts2008. Right-click on the file and hit edit. Scroll down to the end of the file and add path to the Warper. Save & close.
6) Open scripts2008 and compile.
7) If you want to change the entry of Warper, open Warper.cpp and scroll down to the end, until you see "mgr->register_item_gossip_script(65001,gs);" Change the number and compile.
The NPC flag for Warper should be 8192, but please check OpenAscent wiki to be sure.