Hot on the heels of MozillaBuild 1.2, RC1 of the Build Team's Linux Reference Platform is available in the form of a VMware Image. It should work (read: has been tested with) VMware Workstation 6, Fusion, and Player. With this image you should be able to boot it up and download/compile Mozilla without any further configuration.
This image is what most of our Linux Trunk/1.9 Tinderboxen run on. It is essentially the "Linux CentOS 5.0" platform + "Buildbot Linux" platform. (Those pages are messy currently, and should be cleaned up soon.) Default usernames and passwords can be found here.
Thanks to Preed for originally creating the reference platform.