I have just started to use CruiseControl.NET.
With no prior knowlege I was able to get it up and running with a single test project using MSBuild, MSTest and Team Foundation Server (i.e. CodePlex) in a couple of hours. I posted a bunch of links to useful resources here Devsta 2008 Day 0: Source Control and CI
I can't help on memory footprint as my project was pretty small. I can tell you that while it's not doing anything (i.e. most of the time) it is using ~5MB on my system. In fact the Tray Icon notifier that comes with it takes up more memory than the service at about 6MB. That goes up when it does stuff of course.