I realize this has been documented elsewhere, but I had a hard time finding it, myself, so I thought it might be useful for me to share my story.
Dell Mini 10v, 10.6.2, Bios A05, Netbook Installer 0.8.3RC4.
First time (since installing Snow Leopard) I plugged my hackintot into the classroom projector I was fooling with, I got vertical bars on the 10v. I downloaded an old DellEFI and extracted out the "mirroring" command (right-click on DellEFI and hit "Show Contents." Then you can search for it). As has been suggested elsewhere, I opened a terminal and typed "mirroring off" but did NOT hit enter. Connected the projector, waited for the vertical stripes to reappear... they didn't.
I tried hitting Enter, but by that point my 10v was completely frozen. I tried fooling with various permutations of the "mirroring" command, but no matter what I did, the end result was always the same--a frozen netbook.
Ran NBI 0.8.3RC4 with the mirror-friendly kext option selected. Now it mirrors great (at 800x600, but that's fine--if I'm mirroring my display, I WANT it to have the same aspect ratio as the projector). I haven't yet tried extending the monitor, though.
Anyway, I'm happy. Very, very happy. This laptop was purchased to go with me to academic conferences where I'd be giving presentations. Now I can actually USE it for this purpose.