If it is a late 2006 model, you need 200-pin 667 MHz PC2-5300 DDR2 SO-DIMMs, also know, that the maximum is 2 GB and the Mac mini you have probably has two 512 MB modules, thus you need to buy two 1 GB modules to get one more GB of RAM.
The same applies for an early 2006 model.
You can find a guide here or on YouTube and RAM can be found on Newegg or many other vendors.
Thank you! You have been of great help. New to this site so I don't know if there a way to leave a rating for you or something , if there is tell and i will do so.
Since the Mac mini has only two RAM slots and supports 2 GB of RAM, it is safe to assume that it supports 1 GB per slot, otherwise how would one get to 2 GB with less than 1 GB per slot with two slots?