First thing to try is to change the Repeat rate for your keyboard. Do this in the Keyboard Applet in the Control Panel. Don't know if you need to slow it down or speed it up, try both. It also should not take much of a change.
The other reason for this hitching in your walk is background apps causing the CPU to lose focus. If the above does not help, then do a strict clean boot (the following works for all MS OS's)
http://support.microsoft.com/kb/331796
Last but not least, make sure your video drivers (and motherboard drivers) are optimal. For the motherboard, that means the latest drivers from their website. For the video card, that would be the last stable version, for AMD/ATI that is 12.3 (which is not the current version by a long shot) for Nvidia, not sure.