Intel Core 2 Duos aren't hot nor are they power hogs. Core 2 is based off of the highly successful Pentium M (Mobile), not the hot Pentium 4 Netburst. They are cool and quiet. They are more power efficient than AMD and materially faster. Refer to Tom's CPU charts to quantify. My Core 2 is running at 35 C right now on stock cooling.
Dual core will help you with gaming indirectly. I enjoy playing DS2 with my friends online. We use Microsoft Messenger or Team Speak to comunicate via voice over the internet. I use an antivirus program with realtime protection.
So if you are playing games by yourself, and you turn off your virus scanner, and everything else, dual core won't help.
If you play games online, and use some program to talk to your friends, it will help a lot. Reason: one core is 100% committed to running your game, the other core can use its CPU cycles to take care of the other tasks, such as voice communication, and virus scanning.
On my old Athlon 2100 XP gave me Duengon Seige 2 frame rates of 35+ without a using Microsoft Messenger voice chat. With Messenger voice chat running my fps went down to 15. Obviously thats an older processor, but its also an older game. Do you think playing FEAR on a current single core processor with voice chat running could run better if that conversation was being processed by a separte core? I do.