Message has replaced my iChat after downloading an application for Message.

I was trying to hook my iMessage up to my computer and was told all i needed was a program called Message which should have already been on my computer but wasn't.

I downloaded the application and installed it and now its replaced my iChat and I can't get iChat back.

I've tried going through software updates to try to aleviate but my computer keeps saying 'none of the selected updates could be installed' after taking 15 minutes to download and install.

Please help.