I have a Minecraft 1.8.1, non-Bukkit server (Using the .exe and nothing else) and I wan't to add some mods. Can I do that? if so, how? or do I need to switch to Bukkit?
Also, a friend and I have spent a LONG time on my current server so I would like to be able to changeto a Bukkit server without losing our progress.
Best Answer
It really depends. Are you looking for a server with mods, such as Tinker's Construct or something along the lines of that, or are you looking for a server with plugins, like WorldEdit, WorldGuard, Essentials, so on. If you are going with the first option, your best bet will probably be using Forge, or some modpack that you can find on the TechnicLauncher, ATLauncher, both having easy server set up, assuming you know how to start up a basic vanilla server. The second option, Bukkit, may not be the one you are looking for. Bukkit does not work with mods. However, there are plugins out there to customize your Bukkit server, but those are more for server functionality, not like new blocks or anything. Bukkit still revolves around Vanilla Minecraft.
Your next question about copying your world is also dependant on which option you choose. You can certainly easily copy your world over to Bukkit, as it is still Vanilla-based. Just copy the contents of your world into the world folder with your server jar, and you should be fine. With the modded server, it depends on what mods you use. If you use something that involves terrain/world generation, you may ruin your world with that.
Looking back at your question, I think that you mean mods, so copying your world over may not be the easiest task...