I found this quite an easy proposition to get up an running, I hope you find it valuable:
(1) Download & Install Indiana (preview2 at this time)
- download the CD ISO image from here http://opensolaris.org/os/downloads/on/
- set up a new VM in VirtualBox which mounts the ISO image of Indiana and start the VM
- note: ensure you have adequate memory and disk space ( at 600MB RAM, 5GB disk space )
( this should boot you into a LiveCD instance of OpenSolaris )
- double-click the install icon on the desktop and you are away...
(2) Download the AE network drivers ( the only glitch in the seamless process so far )
- use the ISO for convenience sake: http://blogs.sun.com/alanbur/resource/ae-2.6.0a.iso.bz2
- shutdown opensolaris, mount the AE ISO image instead and Start the VM
# cd cdrom/cdrom0 ( this should get you to the AE tarball and follow the steps in README.txt as root )
# make install ( instead of "make" in Step 6 in the README.txt )
# ./adddrv.sh
(following the rest of the steps will cater for dhcp and make sure your settings stay around on your next reboot )
** in about 5 seconds the kernel autodetected my network settings from the VirtualBox NAT interface and i was away... 
( credit to the blog entry here for kick starting things for me - http://blogs.sun.com/alanbur/entry/kicking_both_tyres_together_virtualbox )