Ok, I learned something from personal attempts to make a server. If its just you and your friends go ahead and make a server here is how: wiki.bukkit.org/Setting_up_a_server however, if you want to make a popular server you are going to need to buy one. Making your own server will make the run time inconsistant, meaning every time you shut down your computer, your server shuts down. Also, flaunting your IP address around the internet is risky. It exposes your computer to hackers. If you purchase a server it means that you have to do minimal set up/ terminal scripts, have a consistant run time, and you will be safe from hackers.

Download a Mod for MultiPlayer? I really don't know :P

i can help you