Step 1:
If you are on a router, you NEED to port forward, or else this will not work
Go to DynDNS.com: DNS Hosting, E-mail Delivery, VPS Hosting and Other Services and register an account if you haven't already.
After you make your account log in and go to 'My Services' and find Host Services and create a Dynamic Dns host. Make sure you click use auto-detected IP address and select create wildcard.
Step 2:
Go to the folder C:/windows/system32/drivers/etc/" and open up the file 'hosts'. In the hosts file, write your internal IP, put a space, and put the host you made with DynDNS. Repeat that with your external IP. You can do it with 127.0.0.1 as well but it is not necessary.
Step 3:
Go to apache friends - xampp for windows and download xampp. After it finished the download you must install it. If you are on Vista, I recommend installing to somewhere like my documents because of the security vista has.
Step 4:
Find your database folder in your WoW repack, open it, and copy and paste the contents in your xampp folder in xampp/mysql/data. Delete whatever is already in that folder.
Step 5:
Go to your database editor and click manage users. Create a new user and leave the host at '%' and fill in the other details to your liking. Create the account, and all the person connecting remotely should have to do is put in 'yourhost.dyndns.com' or whatever your host is as the host name and log in with their account.
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Sorry if this is pointless, or if I left anything out... This is my first guide. If you need further explanations, just post it here.