Or PHP could be used, if you know how (I'm thinking about it too >_>)
The gist of my idea is make it add the message by accessing "send.php?m=" & MessageBox.Text - and that page uses $_GET["m"] to get the message and add it to a database (I could, and probably should, use an array but I only really started PHP, never went far past SQL).
Then, every ten seconds or so (or on a manual click limited to once every five seconds to prevent sidetrack DOS attacks) it downloads "readmsg.php" which returns the last fifteen messages in a format that the application then parses into the message bank.
Of course I'd have to sanitize the inputs and the like too.
However, using PHP to do it like this I could add certain other functions like username/login use, web control panels and even direct web access (which kind of negates the point of an external exe) to the chat.
At least that's the idea, I know I could probably do it but I'm not sure if I can be bothered. Plus it's a bit hacky but according to Rich (or was it Ashley? I'll have to find that post D: ) it should work, because apparently the download object gets the output of the PHP script.
Anyway, all the PHP stuff you'd need to do it that way can be learned easily at W3Schools and doesn't cost anything. The biggest problem you could possibly encounter would be finding a host that would let you do it without charging you a fair amount.