OWC Guide: Find out what Mac mini you have:
  1. Click the Apple in the top left corner of the Mac OS X menu bar.
  2. Select "About this Mac".
  3. An overview pane will appear that lists your processor and memory information.
Below are two examples with the processors highlighted in red:

PowerPC Intel

Note: 2005-2008 models have FireWire 400 and DVI (IDE optical) ports.
2009 mini models have FireWire 800 and mini-display (SATA optical) ports.

Note: If your Mac mini utilizes either DDR or DDR2 SDRam, the options are for your Mac mini. If your Mac mini
indicates DDR3 memory, then these options are not correct for your Mac mini model.