Doublechecking ... your system specs is showing that you're using Leopard (10.5.8). Is that the case? If so, I'm afraid you can't get the tool ... it's just for Lion systems that don't have Java installed, as per the following document:
I tried to download the Flashback malware removal tool. The software will not update and the error message will not send - I get an error message with that too. Is there an online fix or do I have to take it in?
As b noir has said, that tool is only supported on certain Macs running the Lion OS. If you are actually running OS X 10.6.8 or above, check Software Update for what you need.
If you are still running OS X 10.5.8 Apple no longer provides support for you. If your iMac is a PPC, then you cannot be infected by any known variant of Flashback. If it is an Intel Mac and you are certain that you have been infected then the only tool I currently recommend is this from F-Secure: http://www.f-secure.com/weblog/archives/00002346.html.