I want to prevent sending file on hotmail/gmail accounts. Is it possible to track windows messages and hide file upload screen?
I assume that you mean you are on a network and want to stop people at work using it?
if that is so, then you will probably have to configure your proxy to filter gmail/hotmail page requests and remove the HTML that provides those options.
Try to find some documentation about the proxy you use, see if you are able to make modules and/or plug-ins
If you just mean on your own computer, you can get extensions for browsers like Firefox and Chrome that let you do a similar thing. It will edit your hotmail/gmail page to remove the link to add attachments.
You might be able to push this sort of patch out via AD but I don't think you can lock it in, people will be able to disable/un-install the block. It would get applied each time they log in, but if they want to, they can still remove it each time. Only problem is IE which has not extensions/plug-in system.