lilybuntu confusion

[Mark Polesky]

regarding this...
http://lists.gnu.org/archive/html/lilypond-devel/2009-06/msg00294.html
http://lists.gnu.org/archive/html/lilypond-devel/2009-06/msg00303.html

Jonathan Kulp wrote:
> After making the .iso I tested it in Sun VirtualBox OSE and
> everything worked perfectly. Here are the exact steps I
> followed (see if you think they're noob-friendly enough):
>
> 1. Install the OS in VirtualBox, then restart the virtual
>    machine and log in
> 2. open a terminal
> 3. open firefox
> 4. Get lilypond source code from git by copying the terminal
>    commands in CG (have to use Ctrl+Shift+V to paste into
>    terminal)
> 5. run ./autogen.sh, then "make all" and "sudo make install"
> 6. cd Documentation/user
> 7. make doc
> 8. use Evince to view pdf output

Please forgive my ignorance/ineptitude, but I'm stuck on step 1.
Which OS do I install in VirtualBox, and what do I do with the
.iso that I downloaded?

- Mark