I still use an ergonomic keyboard (clone of the MS natural - with some differences I like) from 1997. Its SOOOO Old, its not even a PS/2 Keyboard! Its an AT type, but with a PS/2 Adapter plugged into a 3' PS/2 cable (because the AT+PS/2 adapter is about 4" long and heavy - don't want to break PS/2 port).
You need to:
A - read some reviews on gaming & other keyboards you're looking at.
B - FEEL the keyboard first, before buying.
Much of what MAKES a "gaming" keyboard is the style and that the keys light up. Make sure you actually like the keyboard before you spend $50~2000. Okay, only the LED keyboard is $2000.
C - MS doesn't really design their Sidewinder products, they pay RAZOR to make xbox/Sidewinder looking products.
MS keyboard review:
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=237&Itemid=65 I think the snap-off to either side numeric keypad could be handy.
But the Timberwolf is what I would call a TRUE gamer keyboard:
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=218&Itemid=65 this design is actually over 3 years old. They also make a version with JUST the WASD circular pad.
So you may want to check out recent Logitech and Razer reviews.
But when I play games, I never use WASD to play.