I did have the same error about six months ago when my own Toshiba was new. I did the fallowing but I have some questions for you.
Did you disable any of your other security programs before you tried to install AVG? If not disable ALL of them.
Was Symantic and Mcafee uninstalled before you tried to installed AVG?
If you still have them loaded:
To have these removed I would recommend that you use Revo Uninstaller.
What, if any, other security programs that you have loaded?
AS for any other junk that you will need removed I would use CCleaner and the registry cleaner part of CCleaner. Make sure to save a back up of the registry!
Hopefully this helps you out in some way.
I purchased a Toshiba notebook, with Vista 3 weeks ago. I loaded AVG for protection. My computer had symantec and Mcafee already loaded. The AVG program turned out to be a "free Trial" version of AVG. I did not notice this until I received a message saying that it had expired. There was a survey that asked what program I would be replacing it with and I selected AVG Free. I can not load the free version. I continue to receive an error message: Local machine: installation failed
Error: Action failed for file avgtdia.sys: starting service....
Please help. I also would like to remove Junk from my computer but can't identify which files have the junk.