Adding RAM to a Mac Mini

At this moment in time, your system has 512Mb RAM, and since it only has one slot (unlike later models which had two), it can only take a maximum of 1Gb, thus the only option open to you is to remove the existing 512Mb module and replace it with a 1Gb unit. Increasing RAM to 1Gb will give you better performance in general, though not startlingly so - more improved smoothness of use.

As to how you go about the upgrade, getting in the mini is a bit tricky and requires use of a couple of very thin putty knives, as shown in the video linked to on the page at http://eshop.macsales.com/shop/mac-mini/ It's not for the faint-hearted, but it's pretty easy really. Unlike later models where the memory is under the hard drive and thus requires some additional disassembly, on your model the RAM is a single slot on the edge of the logic board and can easily be accessed with just the top off the system and no further work.