The op-amp circuit that Octavio drew is one that got me in trouble once.
 While the temp sensor is variable by temperature, the subtraction circuit is
sensitive to power supply voltage.  If the supply varies, so does the
temperature reading.  Also, if the temperature sensor is not mounted
remotely, care is required that all the resistors and other components don't
introduce an error with temperature drift.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850
Fax:  (716) 328-1144
e-mail:  Mcorio@aol.com

***** Designing Electronics For Research & Industry *****