http://www.gamesas.com/topic/1279548-archery-magic-range-limit-fix/page__fromsearch__1
Add this to your skyrim.ini in your My Documents\My Games folder (as in NOT the one in your Steam folder):
[Actor]
fVisibleNavmeshMoveDist=8192.0000
The max value is around like twelve thousand.
And while you are at it, add this:
[Combat]
f1PArrowTiltUpAngle=0.7
f3PArrowTiltUpAngle=0.7