Apologies for posting a direct link in my initial posting (newbie error: D'OH!). Thanks for putting me right about that.
Txnnok: >click< The penny just dropped! You mean 'is Xpadder compatible with my "extended" keyboard?' OK, you sound like a technical person, so speaking as a Windoze programmer, I'd take a punt and say 'yes' to that: because your SteelSeries keyboard will work (as far as software support for it in Windoze goes) in one of two ways.
1) A replacement keyboard driver, probably a custom WDM driver DLL, specifically to support any 'extra' keys on your keyboard. If you open REGEDIT and look in HKLM\SYSTEM\CurrentControlSet\Services\Kbdclass\Enum; then also open Device Manager and look at each device in Keyboard, and click Properties, Details tab and look at the Device Instance Id and the Hardware Instance Ids listed there: (deep breath!)
you should be able to marry the two. And if you hunt nearby in the Registry for ...\HidUsb\Enum and ...\Mouclass\Enum, you can do the same trick with device/hardware Ids for all your Mouse and HID controllers as well. Anyhow... you should be able to work out if it's a 'standard' MS keyboard driver or a custom one written by the hardware manufacturer.
OR
2) A utility (usually housed in your System Tray) written by your hardware manufacturer which supports the 'extra' keys, and which has to be running and active for the keys to 'do anything.' Dell used to use this (maybe still do?). Note that any such utilities will be doing EXACTLY what Xpadder does, except that they're 'reacting' to non-standard ('extra') keyboard keys, rather than gamepad button presses.
Either way, Xpadder should co-exist just fine. In effect, what it does is ask Windows where the current keyboard handler (usually this is the keyboard driver) is, then 'chains itself on' to that handler, so that it can 'send' keystrokes the same as the hardware would. So if your keyboard uses method 1) above, no problem.
But the really neat thing about this technique is that you can 'chain on' more than one 'fake keyboard' in this way. Hence, if your keyboard uses method 2) above, when Xpadder asks Windoze for a link to the keyboard handler, Xpadder will 'chain ahead of' the keyboard utility: which will then itself 'chain on' to the actual keyboard driver, passing on anything 'incoming' on the assumption that it has come from the real keyboard hardware. And so once more, should be no problem. It's also why I'd predict that the response to your gamepad from Xpadder should be as instantaneous as pressing a real keyboard key would be.
Actually, about the only way you could have a problem is if your keyboard's support software (driver or utility) is badly written and/or has been written to be 'hostile' to other keyboard-related utilities. This is so highly unlikely that I think you can safely discount it as a possibility.
Sorry if any of that was a bit overly technical: that was the simplified version! Hope it helps some of you folks out there understand how all these gizmos and widgets can co-exist as well as they do. Please ask if anything was unclear.
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BFN and regards
Cad Delworth CEng MBCS CITP