... Is it too old?
Your MacBook will either meet the hardware requirements for Snow Leopard, or it won't. Check the requirements here: http://support.apple.com/kb/SP575
- Mac computer with an Intel processor
- 1GB of memory
- 5GB of available disk space
- DVD drive for installation
You may be able to buy Snow Leopard from Apple. Call 800-MY-APPLE and ask if it's still for sale. When it was available from the online Apple Store, it cost about $30.
If Apple no longer sells it, buy it from your favourite software vendor.