I think that was sleslie and it was in Google SketchUp I think, which has a free version. I used it to create my masterplan of the Broadgate/Cathedral area.
http://sketchup.google.com/download/
It's decent for simple stuff - it just doesn't do rendering very well. As long as you're not bothered about it looking ultra-realistic it'll do the job. You can also import pics from google earth so you can use it as a template for an area without having to measure it all out
Here's the thread http://www.skyscrapercity.com/showthread.php?t=581976&highlight=sketchup Post 113