question about brake caliper piston?

Hi,

i got a 93 prelude VTEC - i noticed the other day that the front calipers seemed to be gripping the front wheel rotors when the brakes were not applied. the front wheels have been getting hot when driving and the gas mileage seems to have dropped over the last couple of weeks.

anyway i took off the calipers and used a C-clamp to push the caliper pistons back inside so they were flush with the caliper housings. i then put both calipers back on and of course the wheels spun smoothly at this point. when i pumped brakes to get pressure on brake pads again, however, they were still not releasing all the way. do i have bad calipers? what is actually failing inside of the caliper that the piston will not retract from applying pressure on the pad?

if i have to change the calipers, what all is involved with this job?

any help would be appreciated,

thanks...