It seems many are using lots of force (30+ pound) magnets. I'm sure you can make hardrive magnets work, but the best way to find out would be to make a test bot and try it.
We are using a pair of these:
http://www.kjmagnetics.com/proddetai...884DCS&cat=173
Only ~9 pounds of maximum pull from each, but plenty of pull to provide the traction needed for the bot to climb.
In designing the magnets: create a system in which you can change the distance from the pole easily. For me, it was just add washers.