Regarding Civ and folding. Folding will release the clock cycles, but it keeps the memory allocation, at least as far as I'm able to tell. That's why Civ may run slower on some systems.
On another front, I am replacing my current desktop (1.57 GHz Athlon w/266 MHz frontside bus, 512MB ram) with a laptop which has an Intel Dual Core at 1.83 GHz/667 front side bus (I think..maybe 566) and 1GB ram. Yeah, I know it's not the fastest processor in the world for laptops, but it's still faster than what I have. The dual core is what I am excited about as I should be able to play civ just fine while the second core is still crunching away.