I am having problems un-installing iMessages(Beta) and re-installing iChat

Could someone help me with an answer to my problem. I installed the (BETA) version of iMessages, and now I want to un-install it and get my iChat bck.

But, I am running into a problem. Each time I to the the iMessages menu, and select "Uninstall Messages Beta" it begins the process by looking up software, then I get a window saying..."The software is currently unavailable...you can check for the software later by choosing Software Update from the Apple menu".

So, I am at a loss, and not know how to fix my problem. Is there anyone out there that can help?

I am on a new MacBook Air, 2GHz Intel Core i7.

Thanks,

Tim