Q: I have an old Macbook 2.1 GHz Intel Core Duo, 1GB 667MHz DDR2 SDRAM, Model Identifier MacBook 4,1, OSx version 10.6.8. I need to know if it is a mid, early, or late 2007 model so I can purchase and install the correct memory cards to upgrade it

If you go to crucial.com, you can download a scanner that will report back to Crucial the stats on your Mac. They will generate a report with all of the option that are available for your Mac.

One way to check is to go to http://www.everymac.com and click on MacBook and find the machine that meets your specs, that is, MacBook4,1 and you will see the year.  You can use that at sites such as OWC, http://www.macsales.com and Crucial, http://www.crucial.com to find exactly the recommended ram for your MacBook.

There are a bunch of way to skin that cat.

One of the things I like about the RAM scanner from Crucial is that there is less chance of error that way. Some times the everymac site can be a bit confusing.

Edited to remove lookup errors.

Your Macbook 4,1 is actually  a 2008 model. Here are complete specs http://www.everymac.com/systems/apple/macbook/specs/macbook-core-2-duo-2.1-white -13-early-2008-penryn-specs.html

As noted above OWC or Crucial are the best places to buy mac ram.