This should work:
float tempvoltage = analogRead(tempsensorpin) * 5.0;
tempvoltage /= 1024.0;
float temp = (tempvoltage - 0.5) * 100;
As long as you have a 5v arduino!
if you are still getting readings of 293+, then have a close look at your sensor, you probably have an LM335 instead of a 36GZ... In that case, simply add the line:
temp = temp - 273.15
to the end of the above.
I happen to have both of these sensors in front of me