The first line of the documentation reads...
Real Temp is a temperature monitoring program designed for all Intel single Core, Dual Core and Quad Core processors.
You may want to clarify that it's only the Core and Core2 CPUs as they are the ones with the thermal sensors in them.
Yes, I wasn't thinking and tried it on my Pentium D
At least it was nice enough to tell me it wasn't supported without being insulting.