Given the limitations of my Mac laptop, what piano software would work comfortably without stretching the limits of my equipment? (Mac OS 10.6.8; 2 GHz Intel Core 2 Duo; 1 GB Ram) I play a Yamaha CP300.
You will almost certainly need more RAM.
Based on your 2 GHz Intel Core 2 Duo processor you must have a Macbook instead of a Macbook Pro. I don't believe the latter was ever sold with that processor. If your Macbook originally shipped with 1 GB RAM it should be a MacBook2,1 or MacBook3,1. Check the Model Identifier in the System Profiler to see which it is. The former is limited to 3 GB and the latter 6 GB of addressable RAM, although Apple officially only supported 2 GB and 4 GB respectively.
Your processor meets the minimum requirement for the virtual piano software I am familiar with, but just barely in some cases. That may cause limitations (such as having to use more latency) depending on set-up and what else you want to run simultaneously with the piano software.
Beyond RAM you will find that the 5400 RPM disc drive (unless it was upgraded to 7200 RPM) does not meet the recommended minimum requirements of most software pianos, and running the sample library on the same drive as OS X is not recommended. The latter means you would need a separate 7200 RPM hard drive for the samples.
Some people here will tell you to ignore these recommendations (some of them don't use Macs), but if you want to follow the manufacturers recommendations you would either need to use an external drive or replace the internal optical drive in your Mac with a 7200 RPM drive (or an SSD but they are quite expensive per GB of storage). Kits for adding a 2nd internal hard drive are available from a number of sources. If you wanted to use an external drive and your Macbook does not have a Firewire interface you would have to use a USB 2.0 external hard drive, which is the minimum recommended external interface for some piano software and not recommended for others.
So you can inexpensively maximize the RAM in your Mac and try some piano software using the single internal drive in your Mac. But since that doesn't meet the manufacturers minimum hard drive requirements, you may have to deal with that issue later depending on what piano you use and what else you run simultaneously.