Trouble Installing DMG Files On OS X 10.0.3


I recently got an I Mac for cross browser compatibility testing and installed OS X 10.0.3, but now I can't install any DMG files. I keep getting an error any time I try to install any of these. I've tried installing IE, Fire Fox & Flah Player for the Mac but they all errored out. I can't even dock these files. Am I doing something wrong?

I'm mainy a PC guy...sorry Mac lovers, so it's entirely possible that I don't know what I'm doing yet. Anybody???
Specific iMac model.
Versions of 'Firefox', 'Internet Explorer', and 'Flash Player' being installed.
The exact error message(s) displayed when attempting to install the applications.
What exactly does 'can't even dock these files' mean? (why would anyone place an installer's '.dmg' file on the 'Dock'? ...)

'... so it's entirely possible that I don't know what I'm doing yet. ...', well ...

Much of todays (MacOS X) Mac software is not compatible with 'Puma' (10.0.x); it is with 'Jaguar' (10.2.x), and most with 'Panther' (10.3.x) and 'Tiger' (10.4.x).

What is known (via a few 'Google' searches):
'Firefox' v 1.0.6 - 'system requirements'.
'Internet Explorer' v 5.2.3 - 'system requirements'.
'Flash Player' v. 7.0.x - 'system requirements'.
10.0 is Cheetah, Puma is 10.1. :) ... I'd go with 10.2 or 10.3 if you can, regardless of what kind of iMac that is...
I had to choose the one web site (to confirm with), where Puma was stated as 10.0.x!
For clarity:
Cheetah (10.0.x), Puma (10.1.x), Jaguar (10.2.x), Panther (10.3.x), and Tiger (10.4.x).

Also, knowing the particular iMac model assists one in determining whether or not a Firmware update may be required, if Panther or Tiger should be installed.