I use these same beads (just a whole lot more of them) for drying air going to an Ozone generator. I spread the beads out on a cookie sheet and bake them at 250 degrees F for 30-40 minutes. Like the post above says - the color change will tell you when it's done. Nuking them in a microwave will work, but they tend to breakdown faster as the water vapor flashes to steam and cracks some beads every time you regenerate. Best source for replacement is buying a pack at Graingers for about $20 (about 2 cups worth per pack).
BTW - Ive found that if you open the oven at about 20 minutes you'll allow alot of moisture vapor to escape, increasing the drying efficiency.
Kai