So, I guess you have a Linux VPS or dedicated server, where you can install whatever you want? Good.

For this, we use the bukkit server.

Here are some instructions:

1. Download CraftBukkit's latest build: CraftBukkit - Recommended Build 
2. Put the .jar in a folder, for this example we'll use a generic one: ~/craftbukkit 
3. Move to the above directory in terminal with 'cd ~/craftbukkit' 
4. Create a new file in the minecraft folder and name it craftbukkit.sh 
5. Edit the file and paste this into it: 

#!/bin/sh BINDIR=$(dirname "$(readlink -fn "$0")") cd "$BINDIR" java -Xmx1024M -jar craftbukkit.jar -o true

6. Make the file executable, either by running "chmod +x ~/craftbukkit/craftbukkit.sh" in a terminal, or by changing the permissions in the file's properties. 
7. Then, in terminal, type '~/craftbukkit/craftbukkit.sh' to run to start the server.  
8. When you're done playing around, issue the "stop" command in console. 

You can run bukkit like described above, but there are other options - you can run the server permanently with an init script or run it with an ASCII interface

EDIT:

Reread your question, could be that I misunderstood. So here is another link to something that should be what you need - Bukkit Webby

Bukkit Webby is a lightweight web administration that is easy and fast to setup It's made of two components :

WebbyBukkitPlugin is a Bukkit Plugin that interacts with Bukkit, read your server log, find all online users, etc.

WebbyRTK is a RTK module that interacts with RemoteToolkit and run the webserver. Even if Bukkit has been shutdown, the webserver will persists and allow you to restart Bukkit.

Current Features

• Server administration based on Bukkit Remote Toolkit (Start / Stop / Restart / Reload)
• Online configuration files
• Online server log
• Backup management (manual backup, automated restore)
• Easy installation : drop the jars and files as any bukkit plugins, setup port, login and password for webby and RTK, and you are done !
• NO APACHE NEEDED !

There are tons of other bukkit plugins for website administration. If my suggestion is not what you want, you can check the plugins.

There is no possible way to distinguish MineChat from a standard client. It's the same with many hacked clients, cracked clients, or similar. From the sound of it, neither of those are a problem, though. A thing that you could do is, if you would be willing to run a Bukkit or similar plugin-supporting server, is have a plugin that isolates players from everything until they move. This would deter anybody with MineChat. I could try and show you how to make it with command blocks, but I doubt you want me on your server, as I am a stranger. I hope that I helped in some way. Have good luck.

EDIT: I may have worded my answer in a confusing way; I'm sorry for that. There would be a way to prevent people with MineChat from doing anything on the server, but there is no way to prevent somebody with a cracked client from doing anything. If you wish me to, I could set up an anti-MineChat thing with command blocks, and I could send the MCEdit schematic for you to put it in your world. That's the best that I can do without just building it on your server.