how do you set up drivers in blender 25?

hey does anybody know how to make drivers for contraints in blender 2.5, like say i have an arm thats set up with both IK and FK controls and i need an arbitrary bone to control the influence of the FK and IK contraints how would i set that up in blender 25 ?

This video includes setting up drivers, not for your specific circumstance but the methodology should be the same

Nice link Richard!
Thank you!

cool, thanks for posting the link, this certainly demistified what happened to the drivers in the new version of blender