Weasel is an Operating System installer similar to Redhat's Anaconda.
When you insert the ESX Installation DVD, this program guides you through the steps of network configuration, disk selection, etc. Or it can perform an automated install based on a script similar to Redhat kickstart scripts.
For installation purpose: Any system that supports ESX 4.0
For running tests: Any Linux System with Python >= 2.4 and pyGTK
To do an install: You need to make an ISO. For an example, see the ESX 4.0 DVD
To run the graphical installer test:
python test/caged_weasel.py weasel.py --nox