Do a google search on the subject and you will find a bunch of utilities that can possibly get your multimedia keys working. I don't remember all of them, I can remember a utility named "hotkeys".
There also are HOWTOs on this on gentoo website.
It might not be possible to get all or some or any of the extra keys on your keyboard. This is because, not all the keyboard have their extra keys working by the standard scan code way...
For example, I could make some of the multimedia keys on my laptop as those keys generate scan codes. Some didn't work, may be because they work thru' ACPI or need to be sent a special command to make them work.
So, it might not be possible to get your MM keys working unless, the manufacturers provide you with the information to make them work, like the special command I mentioned above.
Good luck and happy googling.....