Which one runs cooler: Core 2 Duo or Core Duo?

You're still not running hot, so don't worry. Also, he's running at a lower clock speed than you, which would bring his temps down a bit.

Id say thats normal, i had the core duo T2400 and now Ive got T7400 and its alot warmer than the core duo.

The overclocked CPU in my desktop machine idles above 40 Celsius during the summer. In the winter I keep my house ice cold (I hate paying the gas bill) so it can get well into the 30's Feel lucky your CPU isn't running at 40.

To get technical, the core2duo runs a little hotter than the coreduo as a result of performance increase and it also has slightly lower battery life.
But as pdonket said, his clock speed is lower than yours which affects temperature as well.

[quote=Ignacio49;2647060]Hello. I have an Inspiron 1505 with Core 2 Duo T7200 (2 GHz) processor. A friend has same model (somehow different configuration in memory and HDD) with Core Duo T2350 (1.86 GHz). I thought that Core 2 Duo ran cooler than Core Duo, but in this case it is the opposite.[quote] Clock-for-clock, the Core 2 Duo should run a tad cooler than the Core Duo due to deeper sleep states as well as Intel having a year to a year and a half to further reduce the Vcore on the same 65 nm process. Your Core 2 Duo also has more cache and runs faster. The heat production scales linearly with the number of transistors, linearly with the clock speed, linearly with the capacitance (but you're both on 65 nm chips, so that should be similar) and quadratically with the voltage. So assuming a similar Vcore, yours should run hotter. Run CPU-Z to check both of the Vcores to determine what they're actually running at. Also, the Core 2 Duo may very well have a different heatsink or fan on it. Those temps are VERY reasonable. Mobile CPUs can run at temperatures up to 95-100 C. My laptop's old Pentium 4-M idles at 57 C and hits the low to mid 70s under full load. The P4-M is hotter than many, but operating temperatures in the 50s and 60s are not unusual for laptop chips.