1) download the ChromeOS-Vanilla-4028.0.2013_04_20_1810-r706c4144-VirtualBox.vdi file
2) put vdi file into your virtualbox area
3) create new virtual-machine – type and version are both “other” (this probably does not matter)
4) select use an existing virtual hard drive file and choose the file from the previous step
5) SETTINGS—>System—>Processor(tab) and check “Enable PAE/NX”
6) NETWORKS—>Advanced, change adapter type to “Intel PRO/1000 MT Desktop (82540EM)