Got rid of that double post for ya pal

Rheostats work alright, but thermostats are best. IMO...it basically depends on how much you want to worry about your setup. Rheostats can adjust the heating element but the temps can still vary alot. So you have to 'fiddle' with them in order to keep a more constant temp. With a thermostat, it keeps the heat source temperature constant....no matter what the room temps are.

For $20 more you will have alot less worry: http://www.mgreptiles.com/ZOOSTAT.html