What specific model G4 do you have? If you're not sure of the Apple designation for it, what is the CPU (machine) speed and how many processors does it have?
A G4 QS 2002 model has a max OS version of OS X 10.4 (Tiger).
It originally came with OS 9.2.2 and some version of OS X from10.1.2 through 10.2 (which specific version depended upon when in the production period it was shipped).
Leopard and later can not be installed on it. Reason - Leopard and later require an Intel processor.
OS 9 (any version) can not be updated to any version of OS X. OS X is designed to install alongside any existing verion of OS 9 already present; the two OS's are intended to cohabit on those machines which can use both (in OS 9's case, as an OS or as Classic). No OS X installer will run while the machine is booted to OS 9.
What you probably downloaded from CNet is an OS X upgrade version. Those upgrades require that the machine already be booted to an earlier version of OS X of the same base version (i.e., an upgrade to 10.4.11 would require the machine be booted to some earlier version of OS X 10.4).
There are no free full install versions of OS X legally available, other than the public beta OS X 10.0 and some 10.1 disks released as promos. All subsequent versions require an original OEM disk set (the one that came with a machine and usable only on that specific model) or a retail disk set. Once that version has been installed, it can be updated to the max point version for that base version using download updaters.
There are no download updaters available to take an OS X install from one base version (such as 10.3 Panther) to another base version (such as 10.4 Tiger); such a jump require the use of a retail disk set. This means that if your goal is to have Tiger on the machine, there is no point in acquiring/installing any earlier version. Get the retail set for Tiger and install it.
Your best option is to acquire a retail disk set for Tiger (or earlier version, if that's your final goal).
Such can be purchased from places like HardcoreMac, but prices there are pretty steep.
You can usually find better prices at places like EBay or LEM Swap, but be sure what is sold is what you really want.
Friends and Apple User Groups are other possible sources.
Just want to point out for anyone that might stumble across this that Leopard (Mac OS X 10.5.x) does not require an Intel processor. The first version of OS X to require Intel was 10.6 (Snow Leopard).
Leopard requires an 867mhz G4 or higher though, which explains why it won't work on this Mac (without a couple possible workarounds—I have run Leopard on a 500mhz G4 without issue int he past).
More info here:
what can I upgrade it to? It won't accept leopard (MY RETAIL COPY) and I downloaded a LEGAL jaguar upgrade from cnet which is a .DMG but the 9.2 cant read it, any help would much appreciated. I tried to boot to the DMG but no go, Then I tried to run it and it says no file association
There is no legitimate version of Tiger as a .dmg available from any source, including cnet. Only the Apple Mac OS X Tiger Install DVD through Apple as a replacement disc or legitimate 3rd party sources, such as Amazon or eBay, selling this version.