With all due respect to Kent, I wouldn't just go grab a drill and a bit and start reaming out your peg-holes to fit replacement tuners. A violin peg-hole reamer is the best tool to use, basically eliminating the chance of chipping or splintering the headstock's wood/finish around the holes.
If you're not sure you want to tackle that job, take your guitar to a tech or luthier.
http://www.stewmac.com/shop/Tools/Reamers.html