AVR-Chat

>I've heard of the .Net platform which apparently
>requiers users to download some support file package


I wouldn't worry about that, the same issue was brought up with VB. 
You need the runtimes on your computer for either version to work. 
.NET is a bigger download, but internet connections are faster now as
well.  

What about cross-platform compatability?  Perhaps Java would be an
option as it support more than just Windows(R).  Or better yet, make
it command line or menu driven, and you can use any terminal emulation
software on any computer, no download required.  Not a nice looking
GUI, but it gets the job done, and any computer with a serial or USB
port can do it, even a PDA.

-Don