Deleting Traces of an uninstalled software

Hello,
Am pretty new to the mac environment.

I had installed a file with .pkg extension. Later i wanted to uninstall it...so did a googling and found that drag-and-drop the folder to Trash Can would uninstall the software.

Though , later found that some traces are left behind and doing just drag-and-drop isn't sufficient sometimes.

Came across AppCleaner(As mentioned in one of the articles in this forum).

But this AppCleaner needs the folder to be there but i had already moved it to Trash and emptied the Trash too.

Now, how can i remove the traces left behind.
(I think the Traces may be left behind after moving the folder to Trash Can is because...the second time when i tried to install the same software , in the "custom install" screen it said of Upgrade rather than Install)

I want to be all clean before i start installing the same software for the second time...

Any way out?

Thanks
amal