I've just had a reply on another site that a Core 2 Duo 1.66 Ghz is roughly equivalent to two 1.83 Ghz Pentium Ms -- with the added advantage of being much better capable of running multi-threaded audio software.

So dual core really beats the pants off single core when it comes to audio recording & mixing etc?

Spark

If you definately want to work with a laptop, then a Core2Duo is a nice CPU. The faster the better, but also the shorter your batterylife.

The more RAM the merrier. My Macbook (also with Core2Duo) has 2GB, up from 512MB. That really helps with samples and VST plugins.

Make sure you have the appropriate connectivity since you can hardly record more than 2 channels at the same time on your systemdisk, so you'll want to use an external HDD for your recordings, preferably firewire or eSATA. USB can be flaky, depending on the chipset. I am not familiar with USB performance in that regard.

As far as equivalency goes, the old single core Pentium M is hardly comparable to the C2D CPU when running a multithreaded app. Though nice, a C2D will run past that. In single threaded apps like most, if not all, games the slower clock speed would make a 1.66GHz C2D perform less. Most DAW software can take advantage of dualcore CPUs.