Black model ranges from 2006 to 2008, T Series Core 2 Duo Processor with 512MB to 2GB memory by default.
They are not upgradable to the latest OS X 10.10 but can run 10.7 only.
The earliest 2006 model is 32bit, support up to 10.6 only.
Here is how to find the serial no. http://support.apple.com/en-us/HT1366
I don't think it worth much