I know there's a thread down at the bottom with someone asking about this but I figured it would be better to create a new thread for better exposure.
A guy released a really simple PC mod that allows you to use analog combat with mouse/keyboard.
Just watch that video and it will show you how.
Here's a link to the script file:
It's very simple and it works perfectly. I spent about an hour and it's much more accurate and responsive than the 360 controller.
Currently the only draw back is that you cannot accept quests. This is because you are technically playing with the 360 controller scheme chosen so pressing A or D does not work. So you will have to turn your controller on to press the A button. It's minor but it's worth it.